Why do I feel unlovable and scared after leaving a toxic relationship?

I was dating this guy for almost a year. The relationship was toxic the way we started was toxic. He was in a relationship and basically broke up with her for me. I was lonely and I know it isn’t an excuse but I couldn’t find anyone I liked for 2 years I wasn’t with anyone and I liked him so I looked past it. And it was horrible so I guess I got what I deserved. But I don’t think I’m a bad person I think I just made a mistake. Over the course of our relationship he’s followed and texted other girls stalked a bunch of he’s been exs. Fell off his porch cuz he’s an alcoholic. He doesn’t work , he has no motivation to do anything. Anything I asked he never wants to do and then when we do it he wants to do it over and over again. But when times were good I had so much fun with him we’d laugh and chill and just vibe. I’m really sad because i was looking forward to having a boyfriend on my birthday I was looking forward to building something. But I know I can’t with him. I feel like there’s something wrong with me because he clearly didn’t love me and I’m genuinely scared I’m never going to find a man that’s gonna want to build with me. I have some trust issues but besides that I’m loyal loving a maybe a little clingy but I don't know I feel unlovable and I’m sad i even got into all this in the first place.
Why do I feel unlovable and scared after leaving a toxic relationship?
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