Wanting to Seperate.... But so confused

I am not married but have been with my other half for 6 years. We have been fighting alot lately and are growing apart. He is such a good father and I know he is a good hearted person, but i have lost my trust in him and don't know if I can get over it. The first year of our relationship I got pregnant and that rushed things. We moved in together that year and started are blended family. He has two kids and I have 2 from a previous relationship. I have never really clicked with his kids. They are 12 and 9. There is a lot of bitterness with their mother towards father. The mother has always disliked me because I know she thought her and her ex-husband were going to get back together. But me coming into the picture changed things. His kids always would tell me that there parents were going to get back together and the mothers family would talk bad about me. My "husband" always stood up for me and would talk to their mother and her family. But I just dislike them so much it's sad to say sometimes I hate being around his kids. I would never tell him this and I hate feeling like this but I can't help it. I am nice to the children and never treat them bad but it bothers me that I feel this way. Also the mother doesn't do any kind of paperwork or taking kids to doctors. I have to do EVERYTHING. Sign up kids for school, sports, afterschool programs and doctor/dentist. My "husband" is just as bad as her when it comes to those things. Thats one problem. Next is the first year right after I had baby he cheated on me. While I was at home with ALL of our kids he lied and said he was going to work. (he works evening/nights). He went out on a date with an ex-girlfriend and then went out to the bar. He came home really late that night really drunk. His friend had to drive him home and he started crying. He didn't say anything just told me he loved me. I knew something wasn;t right. So I checked his social media sites messages the next day. And thats when I found out he went out with a girl. The real truth didn''t come out of his mouth till I checked his bank statements and seen the charges on his credit card. Then the whole story of the day came out. The only reason I didn't leave him is because I truly felt he was sorry becuase that night he came home he was a wreck. He said wasn't sure about our realtionship, but now he is. The first year we got together he also started making music on computer and singing (rap). He loves it and it means a lot to him. I hate it and can't stand his music. I am trying to be supportive but it is SO hard. I feel uncomfortable becuase of the whole rap scence. He wants to go out a couple times a month to bars and clubs to rap. Facebook I feel is an open invitation to females and he has talked to certain girls on there that I don't like. He has one friend who he had had sex with before we met and I can tell she is the kind of girl who loves male attention. She gave him a picture of her posing with playboy bunnies in the back when I was 7 months pregnant. I found the pic in his wallet. He says I am over reacting it's just a friend (he forgot about pic) and I tried explaining to him this isn't normal for "friends" to do. If she was just a friend she wounldn't do that. He is a nice guy and he trys to help people out and doesn;t want to be mean but WTF! I told him I will n ot be with him if he talks to this girl. So far 3 times I have found that he is still talking to her. Once he put her under a guys name in his phone and then through facebook. The last time happened this year and he said he did it becuase he wanted to make me mad and knew I would find out. I can't do this anymore. I don't think he did cheat on me again. But this isn;t the first time something liked this happened. I feel he isn't ready to be in a realtionship and he says he is and loves me. I am 30 years old and so over all this I am turning into a depressed angry ***** of a person. I want to tell him I want to seperate, but then I am scared I will loose him forever because he does have a good heart. He has told me before if I leave him we will never get back together. I feel for me to be a better person and a better mother to my children I need to remove myself from the situation. But when I bring this up to him should I tell him I want to live apart and still be together or is it better just to say we need some time away from each other. So we should break up and maybe after 6 months if we still feel the love we can start dating again but live seperatly? Ugh so confused I just know I can't keep living this way we have already tryed talking through are problems and year after year it's the same ****. HELP!! I need advice...

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