Losing hope

Been with my fiance for 4 years...I am 24 and he is 37...it never fails his insecurities take over him and a fight starts because he accuses me of talking to other guys or anything like that and no matter how I defend myself he doesn't listen I'm automatically a liar. Then he leaves...comes back...and everything is better again...I'm so used to it I'm numb...we have a 3 year old daughter and he has a 19 year old son...and for the past 2 and a half years we have been trying for another baby...we had a miscarriage when I was 13 weeks in now I feel like I stress to much for it to be possible...I don't talk about any of this and I felt like I could let go on here...things have gotten a little better with us and we Both want another child...what is wrong with me??