Please help me, cheated on my boyfriend and need advise!!

So we've been together for almost 4 months, since the beginning of
May, but I have know him from the age of 14, I am now 19 and was seeing him on and off prior to being in a relationship. When we first started seeing each other again I never intended for it to turn into a relationship and was delighted when it happened. Since we had spent almost every week together, I stay at his almost every day and at one point we was considering moving in together but after an argument he changed his mind and admitted that he wasn't ready, I accepted this but deep down was always a little bit angry. We went away for a few nights and whilst away I asked to use his laptop to do some flat research(this was when we was looking for a property); he then said he doesn't allow anyone to use his laptop, from that time I was suspicious as to what he was hiding because I know that he used to have nudes of girls so a few weeks later he was asleep and I couldn't settle, his laptop was open I went through it, amongst his pictures I found a screen shot from a girl he goes to church with dated from Mid May, she's 17 and he's 20, she was saying she'd decided that she wanted friendship, I was so angry, I know from his response that he didn't want to continue seeing her but the fact that in the past he's told me he sees her as a sister and that I've told him so many times that she likes him. I woke him up and explained I had seen it, he then told me he'd been doing things with her, I felt physically sick and told him I was going to go and have sex with someone else, he understandably got angry and shoved his hand in my face three times, I got scared and cried and then he apologised and cried and I took responsibility because I know that I went about it in the wrong way. Since all of this we've continued to see each other and we argue on and off. Deep down I've been holding things against him because sometimes I find it hard to forgive. When we started seeing each other initially he was always really interested, would too to me throughout the day whilst at work, recently that has stopped. Anyway, I went out Friday and contracted someone I used to get with on nights out and arranged to meet him at the club with my friend, I didn't want him sexually because me and my boyfriend have a really good sexual relationship, just wanted this other mans attention. So on arrival me and the other man didn't really speak, I got drunk with my girlfriend and then called him. He told me to meet him outside so took my girlfriend with me. Me and him then walked away towards his car and I asked him to look after me because previously I've relied on him to do so on nights out. He put me in the back of his car and got in too. Before I knew it I must have laid my head on his chest and he had taken his trousers off and I was giving him oral sex, he asked for vaginal sex and I refused. After that went back into the club to collect my jacket before going home with my girlfriend. Since I regret it SOOOO much I genuinely love my boyfriend, there's things I tell him I can't tell anyone else but know that it can't really work now. I could never marry him without him not knowing. Feel like hell end it if i tell him. I've since deleted and blocked every man in my phone that I've had a sexual relationship with, I don't want anyone else, I want him. As much as we argue we have amazing times together and on the whole he makes me so happy.

I'm desperate and don't know what to do. Please help me.

Kind regards.