I think it's deep rooted. My dad left before I was born and wanted nothing to do with me, so I don't know if it's that?
Children can't understand normal adult complexities, let alone screwed-up ones.
We are born hard-wired to trust our 'significant adults' as all-knowing. If you, as a child, felt your father abandoned you because you were crap, then this will have infected your understanding of how relationships work and of your worth. You're grown-up now, but your adult self is formed by your childhood ideas.
Did your mum have other partner(s) later? What did she tell you about your dad and why he left?
I had one relationship where the guy declared love v early on and was extremely intense and then dumped me and became v cold and cruel. Then I had a relationship end when the guy just disappeared on me and even though it was a short relationship, that really affected me too.
So these people were screwed up, much like your dad.
I fear never finding anyone else like him. I don't think I could face looking again. He's so lovely that if he lets me down I'd never be able to trust anyone again.
Well, actually - you don't trust anyone now, do you?
If we have no experience of being loved sanely and reliably, then we're not equipped to respond appropriately when this is offered.
Have you heard the expression, "We seek the teeth that fit our wounds"? It means we look for partners we know how to handle ... and, if our relationship history taught us to be rejected, we will seek rejecting partners. This may not be rational but it makes perfect psychological sense. (I was raised by a bully who devalued me, so guess what kind of man I married?!) It's much deeper than 'choice', we actually believe all potential partners are like that.
If your deep-down belief is that all men are rejecting, then you'll naturally act as if they are despite evidence to the contrary. (I honestly believed all men hit their partners, and those who didn't were lying.)
It is possible to fix this. It's heavy going, though. It involves inner child work, which usually scares people off! But IF you want to learn how to relax in the relationships you deserve, this is what's needed.
How do you feel about that?