He's following half naked women?

I get insecure in my so call relationship, my so call bf has been following a lot of half naked women on Facebook. I have talked to him about it, and he told me he will unfollowed them. He did, but he still kept a lot of them, and still continue to follow more. They are not celebrities that he follows, they're just local women, and women that are famous on fbook.

Now, I call him my so call bf, cause he said we aren't official yet, as I have just gotten a divorce. And when ppl ask him if he has a gf, he will tell them he's only talking to a girl.

I've talked to him again about following multiple women, and he told me I'm over exaggerating, and that I need to stop being insecure with myself.

I'm not insecure w myself, I'm just scared that he wouldn't want to be with me cause he found someone better. But he won't accept that. He said I need to learn how to love myself and not be insecure w myself, so I can learn to accept that he's following women on social media.

Should I leave him? Is he right that I'm overreacting?

I considered him my bf cause we live together and we did sleep together. We do things couples do, but he told me we are not official, so idk anymore.