What can be the reasons for self-sabotaging behaviours when it comes to relationships?

By relationships, I mean both platonic and romantic. I'm just doing a bit of soul searching and reflecting on things I've done in the past.

For example, I used to get a weird sense of satisfaction by rejecting girls that showed interest in dating me, even though deep down I wanted a relationship and wanted to give them a chance. Not in a cruel way, just in a "sorry I'm not looking for a relationship right now" kind of way.

I also used to sabotage friendships that were forming before I got too close to the person. Sometimes I ghosted people, acted cold around them, or just didn't go out socially with them. The result was exactly what you'd expect - people just stopped speaking to me and didn't make an effort anymore, just as I hadn't with them.

I've hurt people that cared about me and can't figure out whether it's fear of getting close, fear of showing my vulnerabilities, or something else entirely.