You might be interesting in reading Plato's Symposium, which discusses the topic of love. The views it expresses wouldn't necessary apply to all of Greece, as they can reasonably only apply to the academic elite of Athens, but it does provide some interesting insight into what Plato and friends viewed on love. The work takes it for granted that loving, sexual relationships between two men, or a man and a boy, are the greatest possible relationships.

I am far from a scholar of ancient greece, but based on how I've interpreted and remember the Symposium, the answers are:

1. I don't know either way.

2. Yes.

3. It was expected of all high-class men.

I think a key point to make here is that sexuality in ancient Greece was seen differently than we do today. People today see their sexuality as fitting into a category--homosexual, heterosexual, bisexual, etc. But in ancient Greece, they didn't have these categories. There were appropriate and inappropriate ways to be sexual, but having sex with only women or only men wasn't seen as an inherent quality of oneself. It was just normal for grown men to be attracted to adolescent boys, or men younger than themselves, just as it was the norm for men to marry a woman, have sex with her, and have children. It wasn't good to not get married, because you weren't fulfilling your duty to your family to have children. It also wouldn't have been normal to avoid sexual relationships with men--so much of ancient Greek society was segregated sexually, it would be like refusing to go out drinking with the guys or something. Men hung out together, older men chose younger men as sexual partners and to mentor, and then when the younger men became older men, they chose their own younger men as sexual partners, themselves.

Homosexuality was seen as normal, you wouldn't hide it.