Im a good girlfriend so why does he treat me like this?

[SpecialLove]

Sorry this is long but u have to know the background lol. Me and My Boyfriend have been together for almost six months however we have been romantically involved for almost 2 years.
We started off just friends both of us were in bad on and off relationships and one night when we were both single we slept together. He ended up getting back with his girlfriend while me and my ex stayed separated. Okay so we were in limo land for a while: They'd break up... We'd hook up... and eventually strong feelings started to emerge. Every time me and him would get close he'd get back with her. His excuse was always he just wanted to give her one last chance (well one chance ended up being three) but they would never stay together longer then a week maybe two... this went on for a year or so. I just ended up really getting my feelings hurt allot even though we were not in a relationship. Somewhere in there I also discover he had lied to me about sleeping with one of my co-workers (his best friend) so a little trust was lost. When we first officially decided to be a couple things were great. Then his ex should back up in the picture and we started to fight because she'd do stuff like send me private messages or call me blocked (she'd been doing this long before we got together) and I couldn't figure out why he would want to remain friends with her. They talked every single day five and six times a day, texting, calling... It just got under my skin. Because of this we argued I just couldn't take it. Now I know Im wrong but like I said trust was rocked when he lied to me so I started checking his phone. It was mostly her all over him but he'd always give her some glimpse of hope that they'd get back together one day he told her he loved her just allot of stuff that hurt my feelings. I confronted him and he said she's the type of girl to want what she can't have so if he makes it seem like he wants her she'll back off. Well she ended up calling me telling me everything he'd told her and that they had slept together however I know she was lieing because one I had read his messages and her dates were all lies because me and him have been living together for eight months (she didn't know about six of those months). Her calling me though didn't end there friend ship which I thought was so ridiculous. I ended up seeing a conversation he had with he two weeks after this that was very inappropriate and finally he agreed to not talk to her anymore (and he hasn't). However I still check his messages I have all his passwords I want to stop but I always find something. Like this girl he used to talk to they are friends now (Yes he has allot of girl-friends he used to date or talk to romantically), they flirt all the time and he lets her talk shit about me without defending me at all. I know I have to trust him more but he has to earn that back. There is just so much with these other girls it becomes overwhelming. Now Im a pisces (he's a taurus) so I am sensitive at times and we do fight but mainly because of all this stuff. He says its because I pay to much attention to them (the girls) but he is my boyfriend Im I wrong for that? And to top it all off he used to be so sweet to her so nice and open with his feelings with me he holds back he tells me he's inlove with me but his feelings have been hurt to much so he's holding back. He said he used to pray for a girlfriend like me that Im so much better then all his other girlfriends. Im really trying to be patient with everything but I need some help getting though to him. I know he loves me but my question is if Im the best girlfriend he's ever had why does he treat me like this? Why does he lie to me? Why does he feel the need to flirt and have so many ex's in his life? Basically what do you think is his issue with me and our relationship?

[Gigabitch]

His issue is that he doesn't respect you, your relationship, or himself. He's a bad boyfriend. If you choose to stay with him, you'll continue to have these problems until you wise up and leave.

[steelsword]

What Gigabitch said. I really don't get why women put themselves through such torture. There are guys that do stupid **** like this, like myself for example, and yet women stay with guys like this dude.