My best guy friend's girlfriend?

Ok so earlier this year my best guy friend, Zack, started liking this girl Genevieve. So he was all ways looking at her and smiling and being all shy, and I wanted to make him happy, so I set them up. And it was working out great . . . until they REALLY started dating and he stopped spending time w/ me. I gave him his space for that. But after like 2 months They became one of those couples that are all ways in a fight or something. They didn't have ANYTHING in common any more; he said so himself. And he wasn't as happy-go-lucky and energetic as he was before. So he finally broke up w/ her. And for like 2 weeks he was the happiest I've ever seen him and we started getting along better. Than for some reason I cannot fathom he asked her to get back together, she said yes, and now he's acting all sad again and doesn't want to talk to me anymore. What do I do? He doesn't seem happy when he's with her but he keeps going back!