I've never been one for distrusting...anyone, really....until they've EARNED it, themselves. But even then, I am the forgiving kind, and always seek the good to be had in most any situation.
We all make mistakes, and with that, I always offer a second chance. But, there is a limit.
"Screw me once, shame on you. Screw me twice, shame on me"

You are creating disaster for yourself from your own fears. Perhaps, therapy is your solution to this issue of yours?

You create your own reality...simple as that. And, just like you've said yourself, you are seeking for lies..(that just are NOT there, might I add). Because of your determination of finding these negative influences, you are creating them YOURSELF. I can almost guarantee you that you will not find HER as the cause of your relationship failing....even though you are certainly seeking to cast blame upon her.

We ALL have a past, and those pasts include other persons. However, they are persons of that past = once WAS...past tense.
From the sound of it, this woman truly IS desiring you, yet you refuse this to suceed. You are sabotaging your own self here, and until you put an end to this behavior of yours, you are doomed to repeated disasters.

How fair is this behavior of yours to this woman who is apparently investing herself into this relationship with you? Imagine the frustrations, confusions and heartache you are creating for her.
She repeatedly proves herself worthy, yet you continue to deny her the trust she deserves.....This is doomed to fail...if you continue this pattern with her.
You have to ask yourself....How much more loss are you willing to take because of your fears? You seem to have a definate awareness of this problem..so from there..begin to confront it through therapy?..Seek the root to the issue, and you can only accomplish this with trained assistance. I can't think of anything else BUT therapy, due to the fact of your awareness of this, yet your inability to overcome it alone.

Perhaps, try a different approach regarding this person of her past:
Instead of convincing yourself that he is the successor, (which he is NOT), maybe, convert that negative thought into the positive BY realizing that, (regardless of his attempts), YOU are the one she's chosen....which makes you the obvious successor.
THAT alone should send you some definate confirmed signals.

I wish you the best. Think positive thoughts. She loves you. And love her for that.....love YOURSELF for that.

Shangrala