love woes

i saw Mr. J. yesterday. he finally admitted that he is hopelessly in love with S. it's a crazy story. last year, at just about the same time, they'd been together for a year and he was so in love that he'd decided that he'd let go of his fears and just be happy. and it worked. for all of two months. then his fears came back and he eventually broke up with her. and for months, he's been telling me that it's definitely over, despite the fact that he knows she's probably his ideal woman. and i actually thought he was trying to move on, but it turns out he isn't really. i don't get it. i don't get how, when you know who've found the one, you can let go.