Dating : Relationship/ex insecurity problem

Dating : Relationship/ex insecurity problem

How do I get over the insecurity and anxiety of being dumped and/or left for an ex?? I’ve been dating around for a couple of years now and there’s always some reason as to why a relationship with the person i’m interested in won’t work. I believe i’m an attractive, attentive, open minded, caring, and understanding partner.This past year I dated 2 guys. One guy had just “gotten out” of a 5 year long relationship, moved states, began a friendship with me, i catch feelings, we have regular sex, all while he’s still dating the girl who lives out of state. Whatever, I got played. He was an asshole anyways. Later on last year, I start dating another guy. I fell head over heels for him, and he dumped me a month into our relationship because he wasn’t over an ex that he dated for 7 years and had broken up with 2 MONTHS before dating me (I had no idea about this). Ever since then i’ve been avoiding men and have trust issues to the max. Recently, I started seeing a guy. He’s sweet, romantic, caring, hard working, kind, and not the f*ck boy type at all. We have been dating about 2 months and the anxiety is kicking in. Before me, he dated a girl for 4 years and they broke up about 9 months ago. I believe they’re on good terms and she recently texted him saying she dreamed about him and it made her miss him. He told me about the situation immediately and assured me I have nothing to worry about. I didn’t get upset, but it’s in the back of my mind and the anxiety is eating me away. I know he really cares about me and he says he loves me and he’s the best boyfriend i’ve ever had but I can’t help but feel scared that it’s going to end like the last two did. I’ve expressed my concerns and he understands why ex girlfriends freak me out. I’ve never been in a super long term relationship so I don’t understand the whole ex and having history thing. What can I do to help ease the anxiety??? Are there any coping mechanisms? What are some ways I can help build my confidence in my relationship??