I mean, you yourself said it ;) Most of those "detailed sexual exploits" of Tiberius specifically come from Suetonius (which is what I'm going to address here). The reason I'm focusing on Tiberius is 'cause I've done a significant amount more work with him than I have with Elagabalus, and I have a whole rant about the way Tiberius is treated in Suetonius.

So to start, I'm going to present you, dear reader, with the context of these incredibly detailed sexual exploits (Suet. Tiberius, 41-45 - it's a bit of a long quote, but I did promise context. Feel free to skip, I break it down later, but context is important here):

Then returning to the island, he utterly neglected the conduct of state affairs, from that time on never filling the vacancies in the decuries of the knights, nor changing the tribunes of the soldiers and prefects or the governors of any of his provinces. He left Spain and Syria without consular governors for several years, suffered Armenia to be overrun by the Parthians, Moesia to be laid waste by the Dacians and Sarmatians, and the Gallic provinces by the Germans, to the great dishonour of the empire and no less to its danger.

Moreover, having gained the licence of privacy, and being as it were out of sight of the citizens, he at last gave free rein at once to all the vices which he had for a long time ill concealed; and of these I shall give a detailed account from the beginning. Even at the outset of his military career his excessive love of wine gave him the name of Biberius, instead of Tiberius, Caldius for Claudius, and Mero for Nero. Later, when emperor and at the very time that he was busy correcting the public morals, he spent a night and two whole days feasting and drinking with Pomponius Flaccus and Lucius Piso, immediately afterwards making the one governor of the province of Syria and the other prefect of the city, and even declaring in their commissions that they were the most agreeable of friends, who could always be counted on. He had a dinner given him by Cestius Gallus, a lustful and prodigal old man, who had once been degraded by Augustus and whom he had himself rebuked a few days before in the senate, making the condition that Cestius should change or omit none of his usual customs, and that nude girls should wait upon them at table. He gave a very obscure candidate for the quaestorship preference over men of the noblest families, because at the emperor's challenge he had drained an amphora of wine at a banquet. He paid Asellius Sabinus two hundred thousand sesterces for a dialogue, in which he had introduced a contest of a mushroom, a fig-pecker, an oyster and a thrush. He established a new office, master of the imperial pleasures, assigning it to Titus Caesonius Priscus, a Roman knight.

On retiring to Capri he devised a pleasance for his secret orgies: teams of wantons of both sexes, selected as experts in deviant intercourse and dubbed "analists," copulated before him in triple unions to excite his flagging passions. Its bedrooms were furnished with the most salacious paintings and sculptures, as well as with an erotic library, in case a performer should need an illustration of what was required. Then in Capri's woods and groves he arranged a number of nooks of venery where boys and girls got up as Pans and nymphs solicited outside bowers and grottoes: people openly called this "the old goat's garden," punning on the island's name.

He acquired a reputation for still grosser depravities that one can hardly bear to tell or be told, let alone believe. For example, he trained little boys (whom he termed tiddlers) to crawl between his thighs when he went swimming and tease him with their licks and nibbles; and unweaned babies he would put to his organ as though to the breast, being by both nature and age rather fond of this form of satisfaction. Left a painting of Parrhasius's depicting Atalanta pleasuring Meleager with her lips on condition that if the theme displeased him he was to have a million sesterces instead, he chose to keep it and actually hung it in his bedroom. The story is also told that once at a sacrifice, attracted by the acolyte's beauty, he lost control of himself and, hardly waiting for the ceremony to end, rushed him off and debauched him and his brother, the flute-player, too; and subsequently, when they complained of the assault, he had their legs broken.

How grossly he was in the habit of abusing women even of high birth is very clearly shown by the death of a certain Mallonia. When she was brought to his bed and refused most vigorously to submit to his lust, he turned her over to the informers, and even when she was on trial he did not cease to call out and ask her "whether she was sorry"; so that finally she left the court and went home, where she stabbed herself, openly upbraiding the ugly old man for his obscenity. Hence a stigma put upon him at the next plays in an Atellan farce was received with great applause and became current, that "the old goat was licking the does."

Now for that promised context: Suetonius wrote his biographies in a very specific pattern. They were not necessarily biographies as we know them today, so much as they were also a judgement of the ruler in question: and if he was not a fan, he would ABSOLUTELY include all of the scurrilous gossip that he could dredge up. As a note - he wrote about a hundred years after Tiberius' reign. There's definitely some distance there, and that - coupled with the fact that Suetonius was not fond of Tiberius - means that the reader must read between the lines in this regard.