1. He talks trash.
You may think his admission that his ex was a two-timing b#@$% is a sure sign that he's done with her, but that degree of passion--even if it's in the form of anger--proves that he's still emotionally connected to her.
2. He has nothing to say.
Once a guy has moved past a relationship, he should be able to admit it was painful or say what he learned from it. But if they were together for a stretch of time and he acts all "whatever," it shows that he hasn't truly grieved the relationship and come out the other side.
3. They're best friends.
Though plenty of exes do wind up on decent terms, being BFF with an ex right away is sketchy. If their lives are that entwined, there's a good chance one of them is holding out for a reunion.
4. He absolves her.
Whether she bailed or he let The One get away, it's bad news if he thinks his last love could do no wrong. Since his imagination has reinvented her as an angel, you'll never be able to compete with her halo.
Sources: Russell Friedman, co-author of Moving On: Dump Your Relationship Baggage And Make Room For The Love Of Your Life; Debbie Magids, PhD, author of All The Good Ones Aren't Taken.