It sounds like thing we’re pretty good between you and your ex because you are not over him. It didn’t seem like things ended bad between you guys. Maybe things might have changed with him. Have you talked with him? I would recommend talking to him if you haven’t and see how he feels about you. 5 years is a long time and I feel like your reason for breaking up was not a good one.

As you said it yourself the new guy was just a rebound.  Trust me I’ve been in your shoes before if things were good with your ex talk to him.