Why do I feel like I don’t deserve better?

In my head I know I do deserve better. But I don’t get give it to myself. For example, if a started talking to a guy and he seems great. I get this feeling of being scared and I’ll pull away. I put myself in bad situations and then hate myself for it. (I know I’m to blame because I chose what to do) but I can’t figure out why I feel like I don’t deserve it.
Why do I feel like I don’t deserve better?
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