Point is that he still got laid a great deal and doesn't look at Hawke at all if she isn't a virgin. He doesn't even give Hawke an option to be "Born Again" like he was per say. That in turn makes him a hypocrite as he got a lot of nookie but that's "okay" to him because he "repented" but he doesn't extend the same to Hawke. She loses her virginity and she's suddenly tainted to him no matter what she does even if she lost her virginity before meeting Sebastian.
First, it's not that Hawke is or isn't a virgin. That isn't the problem. Sebastian makes not mention AT ALL about Hawke's romantic life before she met him. He has his past. She has hers. What Sebastian cares about is Hawke's present. And if her present consists of another current relationship, then he won't get involved. To me, this is sensible and practical. He's not going to step on any toes, and he's not going to want to be with a woman who is currently involved with anyone. That is a relationship tactic that many today employs because is avoids drama.
Sebastian doesn't seem to respect Hawke, he knows that she wants to have sex and maybe have children in the future but he refuses to entertain the thought of a marriage between them being anything more than Hawke remaining a virgin and never having sex.
Uh....not if it's a rivalmance. All he says is that an alliance between the Vicountess of Kirkwall and the Prince of Starkhaven qould be the strongest the Free Marches has ever seen, and that he will give Hawke 'no less than a prince'. This is not a man who is insisting on a chaste marriage. This is a man saying that they are going to be forging not just a personal relationship, but a political alliance. There is no way that a marriage between such important people would have an unconsummated marriage, and Sebastian knows that.
The flirting is funny but the romance is a disaster as it's Hawke giving everything to Sebastian, and living to his standards, while he gives nothing up to Hawke, as he already chose to be chaste, and he doesn't live to her standards nor does he care for what she wants but expects her to do what he wants.
Sebastian simply doesn't understand that Marriage is a Two-Way Street, not "My Way or Get Out".
Hawke and Sebastian are never married in DA II. This is not a two-way street. This is an establishment of one.
Hawke is the one who initiates. She is the one who decides to flirt with Sebastian. He was fine on his own, never giving any indication that he thought of Hawke in a romantic fashion. So he is under no obligation to change for her. Neither is she, but you can hardly say that the ball is in Sebastian's court. He lets her know the kind of relationship he is comfortable with. If that's not what she wants, then they can part ways, no harm, no foul.
The order of Seb's romance goes like this:
1. The two meet, go on some adventures, do eachother some favors. The are friends or rivals depending on the Hawke involved.
2. Hawke lets Sebastian know she is interested by flirting.
3a. If Hawke is already involved with Isabela, Anders, Fenris or any of the employees of the Blooming Rose, he gives her a firm 'no'. He is under no obligation to say yes just because he has a racy past. Just because he's slept around in his youth doesn't mean he can't hold a higher standard for relationships now. He never judges Hawke for being in another relationship, he simply says that that's not what he, personally, is interested in.
3b. If, on the other hand, Hawke is not involved with anyone else, Sebastian responds about as well as could be expected from a deeply religious man. He prays and seeks guidance, unsure of how he should proceed. He's obviously attracted to her physically, and she has shown herself to be a virtuous woman for as long as he has known her.
4 Hawke and Sebastian have more adventures, and Sebastian asks for guidance from Hawke, who he trusts as a friend or as a respected rival.
5a. If Hawke has supported Sebastian's Chantry career leanings, then he offers her a chaste marriage before the Maker, the most he can offer her if he is to remain in the Chantry. Hawke can say yes or no to this, and that's the situation. If Hawke wants sex and kids, a friendmanced Sebastian is not the man who will give that to her. Period.
5b. If Hawke has encouraged Sebastian to pursue his birthright and rule Starkhaven, he tells her that once he has his throne, he will offer her his hand. He values her as both a woman and a powerful political ally. So he treats her as such. In this case, it shows how Sebastian holds himself to a high standard as well. No matter how willing Hawke may be, he will not commit her to him when he is still standing on shaky ground. He treats Hawke with the respect he knows she deserves.
6. If Hawke decides to spare Anders, the man who killed Sebastian's spiritual mentor, as well as countless other friends of his, Sebastian leaves regardless of their previous relationship. He will not work alongside a man who has committed such an atrocity, nor will he accept Hawke letting him off the hook.
7. If Hawke kills Anders, Sebastian's relationship with Hawke ends with uncertainty, like the rest of the game. He is not mentioned in the epilogue because it's clear he has somewhere to go after Kirkwall. He has a city to reclaim.
You can argue how well Sebastian's character was written, ways in which his character might have been improved. But how and why any of this makes Sebastian a hypocrite is beyond me. He's indecisive, impulsive at times and waffling at others. Certainly a flawed character. But he always conducts himself with integrity.