How do you get over an Ex?


I broke up with my ex almost 3 weeks ago now. It wasn’t probably the best choice but we decided to stay as friends. I deliberately didn’t contact him so I could try and move on however recently we’ve started talking in a friendly way again. I’ve had Now 4 missed calls from him just this week but have ignored them all. I decided to call him this morning to see what he wanted and he didn’t answer so I sent him a text asking what he wanted. He never replied. He’s asked me to meet him and he sometimes still sends me Xs on the end of his messages. We’ve been through so much and have been close for over 3 years and the relationship ended suddenly because he “lost all feelings” for me. I say I’m over him but from time to time I find myself looking who’s Insta photos he’s like and how much his snap score has gone up. I know that sounds extremely stalker ish but I can’t help it I’m always thinking about him and he’s making it very difficult, by calling me etc to move on. I couldn’t give a shit who he is with anymore and what he’s doing but he’s always in the back of my head. What the hell do I do because I’m not entirely sure he’s over me because whenever someone asks him about me he tells them “I don’t want to talk about it” and then apparently goes quiet which is really strange. Please somebody give me some advice!! Should I talk to him about it?!