SORRY REALLY LONG BUT PLEASE HELP

A while ago, I confronted my boyfriend about seeing his ex messages on his skype and I read them all and they were not appropriate for exes. Talking about meeting up and her moving out here and texting each other, also she mentioned being roommates... his replies were kind of encouraging this...I asked just about talking to her in general and he acted like they just fuckin g said hi. I let it go considering thinking that I was being snoopy and jealous but then while a friend was over with me I asked her opinion and then saw that one of my old friends exs (his friend who's a girl) messaged him on Skype and I never thought of her as competition cause he always reassured me that she was annoying and not his type...I saw his messages to her were ones of saying I was okay with him screwing her as long as I wasn't to see it or know about it and hen wanted to meet up. He also complemented her and reassure her weight by using me..she's thin and I'm curvy with a bit of cushion (210 lbs) and it's always been my insecurity and something Km working on but I felt really hurt that he told her stuff like that. I cried my eyes out and drank a bottle of wine. When he came home I was beyond pissed...he cried to me apologizing and promising to fix it. He said that he was lost and doesn't know what to do with his life and that he loves me and me only.. I took him back but now I'm having night terrors and he wakes me up almost every night because apparently I almost suffocate myself due to my nightmares...what should I do? I love him and we've been together a year and friends for 4...I've never stayed with a guy this long or one never made me feel good...am I stupid and should I leave him? Or can I make this work and how?