Time helps. I had about a year long "relationship" with someone once, I loved him so much, but he just wouldn't commit, wanted to keep sleeping around, I compromised for a while and we had an "open" relationship but it was the fact he kept seeing his ex that killed it for me in the end. (I'll call him ex-bf)
So of course about a year later when I was with (now ex partner - XP) I hear through one of his friends that ex-bf was now back with this girl he'd been seeing at the same time as me, and they were expecting a baby. Oh, and he'd been messing her around like he had me, but as soon as she got pregnant he stepped up to the mark. That hurt. A lot. I didn't want to be with him any more (if I listened to the rational part of my brain) but inside there was this real feeling of that should have been me.
But you know, in time, and especially from the wisdom of lovely MNers on this board, I've come to realise that he wouldn't have changed into a perfect example of a man in those circumstances. He may have stopped messing around, but he wasn't going to fundamentally change who he was. And while he would have been a way better weekend-father than XP is, TBH I don't think I'd have been happy with him in the long term either. So it was for the best.
Also, a 16 year old is very different to having young children. So it may have been a situational thing. Although your man probably was trying to let you down gently by using the children as an excuse. Sorry :( Still, just because one person decides you're not right for them, doesn't mean you'll never find someone else who's even better!
This article is really good.