I need advice please.?

Ok me and my boyfriend have been dating for 1 1/2 years now and we are engaged and plan on getting married in two years when we have the money but the thing is when we dated for about 8 months i was on birth control and it changed my mood drastically and made me bitter and angry and basically a ****** so of course i caught him sending pictures of himself to his ex gf and he would say i love you to her and when i asked him why he said that he still had feelings for her but now he doesn't he despises her and I believe that so i gave him a second chance after that i switch birth control's and my emotions and mood have gone back to normal but then we broke up again because he said that he wanted to date other woman see he is VERY addicted to World Of Warcraft and he wanted to date me plus two girls from on there but later on he realized that what he asked for was really stupid and asked me to forgive him and i did..then just recently i caught him flirting with another girl but she lives in Europe and she plays ps3 online with him and he told me that when you play online games you have to flirt he said he doesn't mean to but he does I kinda gave up and said ok go ahead flirt with other girls if it make you happy because that's all i wanna do is make him happy he got mad started flipping out broke his headset and router so he couldn't get online or talk to other girls after that me and him have been very happy but no i just worry like if me and him are going to last I mean it could be worse he could be flirting with girls that actually live in our area instead of 20,000 miles away but I don't know what to do..I don't want to leave him but trust him and i guess i just need advice from other girls/boys..like over time will i actually trust him? I have no idea what to do like i really want to forget everything that happened because what happened in the past should stay in the past..I just don't know how to forget :(