My point below doesn't seem to have been mentioned in first few pages. [I read up until page 20 so far.]
My guess, why he "doesn't even know why he is still going for you", As you mentioned, it's because you're the only girl in your barkada he hasn't been able to sleep with yet. Kita mo rin with how he talks trying to make you stick with him kasi you are "past your prime", kumbaga what he is trying to say is that he is all you have. Which is not true naman.
Just something to take note of is that bad boys love a challenge. When he finally wins, the excitement disappears and he will begin looking for a new challenge.
Either that, or you're the only person who remotely puts up with him on a long term basis, and while I think that's sad for him, mas kawawa ka to be on this end of an abusive relationship.
Sorry to say this pero time to just stop thinking about him and drop him na. Many other fish in the sea. Everyone deserves someone who will at least treat them right.