So you've made attempts at relationships, only to be overcome with doubt, to the point where the relationship ends.

Residual feelings from your childhood could very well be playing a role. Come to terms with emotions in your past and in your current state. Find a professional to guide you.

If this has been a behavioral pattern stemming years, you seem to be on repeat. So something has to change. You have to get to the source of these doubts. Doubts can be in your best interest, but if they're always around, and you use them as a way to flee, then they can become problematic.