Boyfriend following ex on social media

So the context to that above, basically before me and him got together him and his ex were in a TOXIC on and off relationship, and they almost had a fucking kid, she had a miscarriage... now basically when we started dating I know for a fact he wasn’t following her on anything (I checked) but now all of a sudden I went through his likes on twitter and I found her account, check IG and there she was, they’re following each other :/ I’m sick to my stomach plz someone respond I need help/ reassurance or someone to talk to I am scared