Dancer Story

Hi everyone,
I am just a mixed bag of emotions at the minute and I guess I'm looking for answers and clarity. I had 10 months of a truly amazing relationship met the love of my life and everything was coming together in my life. had returned to study to embark on a new fantastic career and everything was going well. My ex partner was a royal marine reservist, this meant he was based at home but trained away some weekends and might go on courses for one or two weeks. It's came to my attention the reason why he is only a reservist is because he is deemed unfit mentally to be full time (I've obviously only just found this out).
Everything was fine (we had just booked a holiday) until he went away on a three week course, he came back a different man. I took him out for a celebration dinner he wouldn't speak to me for 30 minutes because I was overdressed. The day after we went the cinema, he said it was exhausting him the way I dress and it was like we were on out first date.
There seemed to be regular occurrences like this which I just let go over my head, 10 days later we went on holiday to Menorca, he would shout at me for everything.. moaned I used too much toothpaste when brushing my teeth would take pictures to send to his sister. He was constantly nasty which I thought was because of the demanding course so I made excuses for him. I became jealous of bartenders and women around the pool, I have never experienced it, I think it was sending me a bit mad. We only had sex when he wanted to... one time I dressed up and he basically rejected me. Sorry for all the TMI details! He would sleep at the opposite side of the bed with his arms folded like he was in disgust with me. Towards the end of the holiday he became 'happier' again and we got on good, our day back in the airport was the highlight of the holiday.
We were coming up to our anniversary, I remember going the gym and crying because I was emotionally drained only I didn't know it at the time. I thought it was my fault for losing him and didn't understand why? He was backing off and I was backing forwards.
I finally bought my first car and hadn't driven in ten months since I passed my test. He was so nasty shouting at me telling me I was shit driver, I wasn't committed. I would shake and cry behind the wheel because I had no confidence and was so scared.
He stopped making effort with me, got to the point he hardly wanted to see me which was the complete opposite when he absolutely idolised me and kissed the floor I walked on. We had a chat about him making more effort... he would become so angry he couldn't see me for days. I had gone on a night out and asked could I stay at his, I felt I had lost my going out spirit and just wanted to 'fix' things.
The next day he had took me out for a day out, we literally had the most amazing day out and even went back out in the end to a local pub and got drunk together. It was our anniversary on the Thursday but he wouldn't arrange to do anything. He kept saying a year wasn't a big deal (start as you mean to go on for me). I had become jealous of his relationship with his mum as he bought her wine, chocolates etc for doing a mountain walk where as his anniversary with his gf couldn't make any effort. He even bought the dentist flowers for giving him a free filling - once again jealous, where the hell where my flowers?
It got to the night before our anniversary and I had multiple messages of girls asking if I was his gf. He was on a military dating website... I don't even think it was just that one. I think he was messaging hundreds of girls. What more reading the messages he had told them personal things that he hadn't even told me; it wasn't just sex.
He denied it and then said, "You don't even want to move in with me?" I did but obviously a year isn't long enough to move in with someone (in my opinion). I was a mess I literally felt like my heart was in two and I couldn't breathe. A week later I was drunk, my friend said if you want to me be with him do it. Make him change his mistake there's no point waiting for a break.
So we go back together he promised he was off in the dating websites and he hadn't met up with anyone. Needless to say I'll never find out.
The abuse started to become worse, I was living in anxiety and fear. I thought I wasn't good enough for him I was a failure as a woman. I am only 25 so I can't cook great, where as he's 30 and would belittle me when speaking to me. I just kept thinking the good times were worth it.
I went away for work and he came with me, he had made so much effort until we were out for tea one night and he started being nasty about taking my onions out of my food. More abuse to follow that night.
In the end he said he wanted space from me whilst he was on his course, 4 weeks I didn't hear from him. Until he turned up with my things and said we needed a break. Days later he told me how he loved me and had messed up and regretted it. He told me I was the love of his life, he turned up with a £200 coat, kept saying all we need is time. He had me like a yo=yo. How could I move on when I wanted that perfect relationship back?
Two weeks after Christmas I found out he had dated someone else, he dropped my things off and that was it. Two weeks followed he deleted all my pics off social media and put a new girl all over it. Embarassed to say the least. I couldn't get my head around someone who only wants to be with me and be the love of my life
Why should he be happy? I want to message this girl and warn her but I don't know if I am being spiteful and there will always be more girls.

I am just deeply heartbroken and confused. I feel like hes robbed me for everything I have and now I'm just left there.