<human>: Condense the text into a few key points

So, I used a throwaway for this as my partner & I both reddit, know each others accounts etc. To give some background I was brought up by my mother from the age of 2, not seeing my dad for four years, then him gradually reappearing in my life, however being emotionally abusive on several occasions both towards me and my mother. Typically I would be ditched if he had a new girlfriend who he hadn't told had a kid or whatever so I became fairly used to this.

Anyway, over the past year or so I've met an incredible person, and I'm really in love with her, previously I used to get scared of being hurt before a relationship really kicked off, and in my prior relationship I got cheated on, with my way of finding out being a positive STD test. Grim right?

Anyway, as I've said I've found an incredible person and been able to open up to her about things I've never been able to before. However, I find myself wanting to be incredibly jealous and insecure, I would never, ever demonstrate these characteristics  because it's not fair to punish her for my insecurities. I constantly have bad dreams of her just leaving, or her going away with someone else, and just get trapped in these negative thoughts, particularly about people from her past, such as X, who's good looking, always tried to sleep with her, did fool around, but didn't succeed in going the whole way and they're still close friends now, for some reason I'm incredibly insecure about his presence. Again, as I say I'd never portrait this negative, selfish thoughts to her as she's her own person and I don't want to limit her. 

Basically, I need a way of calming these fearful insecure thoughts, I know I trust my partner completely but I constantly live with this fear and it's just so tiring.
<bot>: Abandonment issues throughout life, been cheated on, in a great relationship but can't seem to calm the constant anxiety fears that something will go wrong. What can I do to help myself/the relationship?