I've only been in 2 relationships: one with my ex and the one I'm currently in so I can say much for men in general.
My ex and I dated for 18 months. He was perfectly healthy. No mental disorders, very smart guy, etc. We were studying abroad and were gonna go together. I brought up the idea but I guess he felt too much pressure from me and a few months into the idea, he said he wanted to go to a different city but same country. Really really HURT me. I took it very personally. To this day, 3 years later, I STILL don't know how I couldn't have taken that personally. Its like hey I need space i don't want to be in the same city as you. really?! So, i would have NEVER been able to move on from that. He ended up breaking up with me RIGHT when we both got to Spain in our separate cities in September. By December, his fb status changed to in a relationship but I know he was talking to her in september. Don't know when things got frisky between them or what but to me, he moved on quickly.
my best friends ex moved on pretty quick too. In my opinion, guys move on quickly. Forget? who knows. Move on, yes.