Polyamorous relationship advice please

My husband and I have been together 3 and a half years and married for 3 of them. We have 2 kids together a few animals and our own place. A year ago we started sleeping with another couple and 6 months ago we started sleeping with another friend and 5 months ago we just decided we both could sleep with whoever. About 6 weeks ago we decided to try and have a polyamorous relationship. Netier of us were really talking to anyone or sleeping with anyone. I decided is ould be okay with this to try and make him happy. We were having problems and I knew I wasn't making him happy and I figured maybe if he was with someone else and happy with them he would be happier with me. I know flawed thinking but cut me slack I'm 20 and this is my longest and most serious relationship okay. Anyway a few weeks ago he really started talking to someone pretty seriously. They've hangout 5 times and he's met her kids. He promised me that they hadn't done anything and that they weren't dating yet or super serious. Well she bought him a phone a couple days ago an we just got it turned on last night. I have his old phone because I'm using it for movies for the kids. Well I've been feeling really off and uncomfortable about the two of them so I read their texts messages. He slept with her the day they met the first time and she kept talking about "gobbling down" his cock and they kept telling each other about the future they saw with each other and needing a minivan for all the kids, She has 2 and I have 2, and talking about him cuming in her and her sneaking into my house and having a quickie while I was running errands and them talking shit about me and my husband asking for videos of her masturbating and her telling her that he's the last guy she ever plans on being with. I broke down crying because I can't handle this I never wanted this and I feel so gross and like he doesn't love me. I woke him up and was balling my eyes out and told him I want it to end between them and I can't do this anymore and that I never wanted this. He responds by telling me I shouldn't have woken him up and that I shouldn't have waited until he liked someone this much and that he doesn't want to hurt her and he is happy with her and doesn't want to end things with her. I'm so hurt and lost and confused and I don't know what to do. I don't want him with her anymore I just want it to be me and him one it was but I'm also scared that he will just cheat on me and stay with her. Can someone please give me advice on what to do. I just want my marriage the way it was...