More ancient magic on the sub - yay! The first thing to say in answer to this question is that, despite what you might read in the sensationalist MSM (OK poetry, but it's basically the same), if you're actually practising love magic in the Roman world you're much more likely to be a man than a woman. Dickie (2000) ran the numbers, and found that, despite the images of this kind of magic in both Greek and Roman creative literature (poems, novels, plays etc) being overwhelmingly associated with women, the data we have for the real world is almost exactly the opposite. Curse tablets that fall into the 'erotic' category are mostly in the 'men-seeking-women' bit of the lonely hearts column, rather than any other configuration (although all others do exist - men-seeking-men, women-seeking-men, women-seeking-women).

Now, whether you're a man or woman, where exactly you go for your potions, curses or charms depends massively on which part of the Empire you live in, and what time period we're talking about. Generally speaking (and I mean VERY generally), magical practices tend to get more complex and professionalised as the Roman period goes on. That means that, if you're living in say the fourth or fifth century, you're more likely to be consulting a professional magician than if you lived a few hundred years earlier.

The other contributing factor is geography. Despite what older (and some current) scholarship might suggest, magical practice was incredibly varied across the Empire. If you lived in Britain, you might not do anything at all in this situation - or at least, whatever you do doesn't leave an identifiable trace in the archaeological record. There is no evidence, so far as I know, for erotic magic in Roman Britain, or indeed most of the North-western provinces. As I said, that might just be that whatever magical rituals people performed to attract an erstwhile lover hasn't left an obvious trace for us to spot, or it might be that they did something unmagical, like turning up outside their house with a boombox playing a Peter Gabriel song - who knows! In other parts of the Empire, particularly Italy and the Greek east, there were many more options, and it's here that I'll be focusing for the rest of this answer.

Broadly speaking there are three options for you, my poor, love-sick friend.

(1) You do something you already know how to do, or that your friends/family have told you about. I think that much of the knowledge about magical practices (and indeed religious ones, if you think there is a difference) in the ancient world circulated within close groups of people, who naturally share advice and guidance when someone around them is in a difficult situation. This kind of basic folk knowledge is not amazingly well preserved, but comes down to us in snatches. Maybe you wear a particular kind of perfume, or an amulet that your aunt's best friend's hairdresser swears got her husband to marry her. This is maybe the kind of stuff we get preserved in things like Pliny's Natural History or Ovid's Ars Amatoria, but I am absolutely certain that there's huge quantities of practices, of varying kinds that are just totally lost to us. Humans are creative beasts, and are very good at adapting, embellishing or just purely making up things they think will work. Whether you (the ancient love-sick fool) think any of this is 'magic' is debatable, and perhaps beyond the point. Ultimately what you're looking for is something that will work, right? (Whether you, the modern person interesting in ancient magic, also thinks any of this is magic is a totally different question, and very much besides the point as far as I'm concerned!)

(2) You go to a local wise-woman/midwife/witch. Whatever you (either version of you) call her is not totally clear, but it's a pretty safe bet that she does exist. Although most of our information about this level of magical knowledge comes from creative literature, it would be strange if there wasn't a small kernel of truth to the images of magical women existing is some form or another. It's possible that she gives you similar advice to the people in category (1) - the kind of folk knowledge that circulates a community has to come from somewhere, and these seem like good candidates. She might also provide more specialised options - specific potions, perhaps a lead tablet or scrap of papyrus with magic words written on it or perhaps a doll made of lead or wax - for you to use in a particular way. These are the kinds of things provided by these women in literature - see, among others, Apuleius, Metamorphoses 3.17 and 9.29, Lucian of Samosata Diologues of the Courtesans 4.4, Ovid, Herodies 4.82-94 for examples. Again, we need to take these descriptions very carefully. They are products of their time, so include a heavy dose of misogyny in that they construct a stereotypical image of dangerous women threatening the sexual abilities and independence of men.

(3) You go to a temple and speak to a 'professional' magician, This one is mostly for Egypt or other parts of the eastern Mediterranean (although later also for Rome and perhaps other big cities of the west). These people might have special training or education in such rituals, using written books of magic. They might have connections to Persia or other exotic places (or pretend they do), and might claim special relationships with gods, demons or other supernatural forces beyond the reach of ordinary mortals. These are the people writing the texts we know as the Greek Magical Papyri - a collection of instruction manuals on a dazzling array of magical rituals, mostly dating from the fourth or fifth centuries AD (some earlier, some later), and all from Egypt. What these papyri were actually used for is uncertain. They can't all be serious, take these two for example:

PDM 14.1190-3: You should anoint your phallus with dung of weasel and lie with the woman. She will love you.

PGM 7.185-6: To get an erection: grind up pepper with some honey and coat your penis.

It doesn't take a genius to work out that both of these must be jokes - anyone who rubs pepper on their penis is in for a nasty surprise, and I'm no expert, but I seriously doubt any woman is going to sleep with a guy who smells like weasel poo.

Certainly some were actually used, particularly the guides on making curse tablets and magical dolls. Examples have been found in Egypt that closely match the instructions in the papyri, which is as close as you're going to get to conclusive proof (examples and references given at Gager 1992: 94, available on Google Books). How far these were circulated around the Empire is also a matter of serious debate, but the influence of this tradition was felt in Rome (see, for example the Anna Perenna finds), and even as far north as Trier. It's possible that by the late empire, Egyptian magicians were travelling around, setting up shop in new cities and offering their services to the local populations. However, it's also possible that these kinds of rituals were becoming common enough to circulate among groups (1) and (2).

So those are your choices my friend. A final thing to point out is the creepy, potentially violent outcomes of what you're asking to do. A recent, thought-provoking article used the rise of MRAs, Incels and pick-up artists to think about ancient love magic, and made some rightly disturbing points. As I said in my introduction, these spells were actually mostly used by men to control women, often using graphic and violent imagery. Perhaps it's looking with too much of a modern, moralising eye, but if a woman has made it clear she doesn't want to sleep with you, maybe you should move on? Even in Ancient Greek, no means no.

Bibliography

Dickie, M. (2000). Who Practiced Love-Magic in Classical Antiquity and the Late-Roman World? Classical Quarterly, 50, 563-583.

Eidinow, E. (2007). Oracles, Curses and Risk Among the Ancient Greeks. Oxford: Oxford University Press.

Faraone, C. A. (2001). Ancient Greek Love Magic. Cambridge (Mass.) and London: Harvard University Press.

Faraone, C. A. (2002). Agents and Victims: Constructions of Gender and Desire in Ancient Greek Love Magic. In N. Nussbaum & J. Sihvola (Eds.), The Sleep of Reason: Erotic Experience and Sexual Ethics in Ancient Greece and Rome (pp. 400-426). Chicago and London: University of Chicago Press.

Gager, J. (1992). Curse Tablets and Binding Spells from the Ancient World. New York: Oxford University Press.

Winkler, J. (1990). The Constraints of Desire. New York and London: Routledge.