He refollowed his ex?

Our relationship was toxic, we argued almost daily. He was jealous, possessive and controlling.
In the 3 first weeks of a break up with my ex, we decided to be friends with benefits, then we got into the argument and stopped talking. We were in a no contact for a week and half. During this time I was feeling good. The no contact really helped me, also he removed me as his follower on instagram and has a private account. I even stopped checking his count of followers.
I felt like I am on a right path until my ex texted my again few days ago. He asked me to hook up with him, than changed his mind, because he still has a strong feelings for me and it wouldn’t help him to move on. He apologised because right now he is an emotional mess. He told me he loves me and our convo ended.
This absolutely ****ed up my healing. I have again started to check his count of followers. My ex followed like 10 new people in the last 14 days. Unfortunately I also know the count of followers of his ex girlfriend and she gained one new follower. She also has a private account, so I don’t know who is it.
It freaked me out, that her new follower could be my ex. I figured if he started dating someone new, I'd take it much better, than if he started dating his ex again. I would feel like my ex never loved me and I was just a rebound.
There were no signs in our relationship that he still loved her. He mentioned her here and there, but it was quite normal.
So how to stop making a negative assumpitons?