I feel sorry for Tate. He was this army guy as someone has said, and then along came Cat and whopped him good and proper, and taught him some pretty exotic stuff. To an army man, that must have been pretty impressive. So he gets this crush on her which eventually develops into love. She's pretty distant and untouchable, so he keeps it to himself, hoping for a softening in attitude as she gets to know him better over time. As far as he knew, there was nobody else in the field (and he HAD been watching), so when the night of the party came, the alcohol loosened his usual inhibitions (as it tends to do), and he gave it a shot. He'd reached the point by then, I think of 'What the heck, I'll just go for it." He was probably thinking he couldn't be any more unhappy than he already was.
Then out of the blue comes Bones into the picture. Imagine his shock (and rage) to discover that all of a sudden, there was someone else, and on top of that, he discovers Cat has been in love with this character he thought was dead--for years
! So what's left for him? Just give up and leave? That's not really Tate's character as I read it. I think he decided it was now or never (he couldn't know it was already too late, any more than Annette did), so he's been employing everything in his power in a last ditch attempt. You can't say he doesn't lack courage!
It would take a brave man to challenge Bones--a master vampire, especially after he discovered what Bones is capable of. He probably doesn't care if Bones kills him in his attempts either. I think he'd feel he has nothing to lose, including his life if he can't have Cat. Given that his whole world fell apart when Bones turned up, I'd have been surprised if he didn't
feel a bit sorry for himself. Look what he lost out on? I too, hope he is able to move on and get past this. I think Tate is a good man.