Ouch. What a bummer. I assume he went on holiday with her whilst still with you, right? That's not on. If it wasn't for that... if he hadn't been spending time with her but had ONLY been contemplating it, then I wouldn't say that he's been a douche, because at least he's owned up now.
But since he HAS (pressumably) taken his thoughts to the next level by acting on them, yes, he's been a douche. And why would you want to chase down a douche, hmmmmm?
You have to get it in your head - as painful as it is - that everytime he was looking in your eyes, he could have been thinking about hers. Everytime you went out on a date, he could have been wishing it was with her instead. Everytime you had sex....
When you stop and think about what it really means that he wants to leave you because he's not over his ex, you'll stop wanting to be with him. You'll still be upset, but the last thing you'll want to do is 'resolve things'. You must realise that you have no control in this anymore. Perhaps you did at one point; perhaps you yourself are not perfect and behaved in ways that made him think of her more - but all in all, it sounds like he was gonna be thinking of her regardless of how you behaved. So what can you do? Nothing.
I don't see the point in talking face to face; how many times do you really need to hear 'I want to be with another girl; in my view, another girl is better for me than you'? What's to talk about? He's already made his decision. I reckon if you meet up, he'll only be doing so to alleviate his own guilt - do a bit of damage control. You, on the other hand, won't really get much out of it. Do it if you feel you have to for 'closure' reasons, but for heaven's sake don't see him hoping you can change his mind. Remember: every time you had sex...
If I were you I would simply cut contact. It's the most personally challenging option, but it's also the best way to turn the attention back onto yourself; you need to take care of YOU now. You've got exams coming up - get on with it. Do the things that make you happy and do not stalk him on FB - in fact, delete him. After all, he did screw you over. In six months from now you'll be well over it. And you never know; he may come to regret his decision, and by then it'll be his problem.