overcoming the (very understandable) distrust you have is not going to be easy. i bet it pops up at times that you're not even aware of it, and obviously all the instances in which you are aware.

the big thing is that you recognize it and you understand that it can hurt you and hurt someone who has a genuine interest in loving you. that's the first step, now getting help to work through your past and avoiding repeating it once you're ready is the next one.

these types of things cast long shadows, so have patience and hopefully you find patient people to help you through it, too.