Toxic relationship

I just need to vent.

So, roughly three weeks ago I built up the courage to break up with my boyfriend of five years. He was my first real boyfriend and I lost my virginity to him. But I felt as though he thought he had some entitlement over me because of the fact that he was my only. And because of that ever since breaking up he has become very obsessive and has been freaking me out. Let me add that for the majority of our relationship he has cheated on me and might have a baby with someone else that he has cheated on me with. Out of fear and insecurity I stayed with him. But when I finally broke up with him I felt so much better. I feel free. But at he same time I don't because social media is a really big influence. I say this because even after blocking him off EVERYTHING he still somehow sees my stuff and posts things that  basically are a reply to what I post. I only know this because other people have told me and showed me. It's just it makes me feel as though I can't have social media(not that it's a necessity) but it's my way of expressing myself and I feel as though I can't express myself because I feel like I'm being watched. And I feel like I have to deactivate my social media and basically disappear. And I shouldn't have to feel this way right? I feel like he has ruined so much for me