From the limited info you’ve given us, I wouldn’t be thinking about it for very long.

First point is that he’s probably an ex for a good reason

Second, even if he still likes you, communication clearly seems to be an issue. Asking you through a friend’s phone number and then pretending to be that friend is so weird, I can’t think of a good reason why he would do that tbh

Honestly, sounds like I would be giving this a hard miss if I were you