Self confidence self distructing my relationship

Three years ago my 9 year relationship with my ex husband and father of my son came to a horrible end. Things hadn't been ideal for a while but I was willing to try and make things work for us and my son. My ex met someone else and rather than telling me he had he made life at home unbearable so I would leave. This included daily verbal abuse and towards the end physical abuse. The last time he was physical towards me I ended up bruised and bloody so I left.... I never reported out of fear (I was a stay at home
Mum studying part time). I was happy the relationship ended but never dealt with the abuse mentally. I indulged in unhealthy habits when my son was at his fathers - drinking too much, sleeping with men too much. The next man I entered into a relationship with ended up cheating on me as well. My self esteem was at an all time low when I met my current partner. He is everything I want in a man. He's handsome, sweet and smart. He's also great with my son. A year into our relationship I was on cloud nine, conversations about moving in together began and I felt like karma was in my favour. I had questioned him about old photos he had of his ex fiancé one night out at dinner and then asked if he still spoke to her. He said no and I left it at that - knowing he was acting strange. That weekend he left me at his house to finish watching a documentary on his computer while he went out. I got curious and noticed he'd left his emails open. I searched the name of his ex and found a large amount of emails between the two. Now they had spilt up 5 years ago and she was engaged to be married. The bulk of the conversations were harmless although he still lied about talking to her. But the most recent conversations the last was a week before were very hurtful to me. He had commented on her latest Facebook profile picture and said she looked "cute" she then replied that he looked happy in his (which was with me) to which he replied "I'm not sure I am". The conversation then went into saying how much they both missed each other and wished they could still see each other. I was heartbroken and was ready to end the relationship then and there. He deleted her from all social media connections and then wrote her an email which he let me see saying I'd seen the emails and it was time to go their separate ways and not
Contact each other in anyway as I was hurt my the emails. It took weeks for me to decide to give things another go but I believed he deserves a second chance. He is a good man and has done all he can to try and build my confidence in myself and our relationship back. I do love him. Since then we have been on two overseas holidays and had many good times but it's nine months later and I still can't help but feel that those conversations happened because he really does miss her and how can I be enough if that's the case. She is very beautiful and must of been a nice person to of been with him. I know that im not horrible looking but not as beautiful as her. I know I'm a good mum and I'm well educated i look after sick people as a job. I know I'm a good person and deserve to be happy but I cannot for the life of me shake my insecurities. I've been depressed post my marriage break down and now suffer from anxiety so bad that I've come
Close to taking my own life. I just don't know how to build my self confidence back again...... I just want to be happy. Not sure what I'm asking but I feel so sad about myself so much. Sorry for the long post