I don’t know what to do

WARNING VERY LONG

So let me start this off by saying my fiancé and I’s relationship isn’t normal.

We have an open relationship and have for almost 3 years. We have done things with others together and but mostly him with other women. Before anyone says anything yes I am okay with this, I am allowed to do things with others also, I just haven’t wanted to.

So my fiancé has always taken at least 45 minutes to “finish” from sex with me. The other women he has had sex with he never even finished. And then he met this one girl.

When she came over I was expecting them to be gone for at least an hour if not more (I was invited to join but I wasn’t feeling it). He comes out about 15 minutes later and says “I don’t know what happened”. So I thought something went wrong and I asked him what he meant. He tells me he’s done already and he doesn’t know why. Immediately I started feeling this sinking feeling in my chest.

No matter how hard I try, what I do, I can’t make him finish in 10 minutes like she did. I just feel like not even having sex anymore tbh. I know that might sound selfish but there’s a reason.

We had thought he had “delayed ejaculation” and he was even going to talk to a doctor about it to try to fix it. But now I see that’s obviously not what the issue is. He told me that she isn’t better than me and he really doesn’t know why it only took 10 minutes.

Every time we have sex now, all I can think about is how I can’t give him whatever she apparently can. Honestly I feel like we’ve been starting to drift apart lately. We argue 75% of the time and the other half is taking care of the kids, him working, or him playing games. Even when she’s not here he’s texting her all day long. Answers her within 2 minutes and she responds just as quick. The other day they were sexting for hours. He’s never done that with me.

I asked him if he had feelings for her and he said no not at all. Obviously besides being a friend anyways. I don’t know if maybe I have PPD and I’m just overthinking things. I just want to feel like I’m good enough to give him whatever she did. I don’t want to break up our family because the kids would be crushed.. we don’t fight in front of them or show any unhappiness in front of them. He says he’s still happy, if not happier, than when we first got together. I know he loves me but I feel like sometimes maybe he’d be better off with someone better. I feel like my kids will hate me when they are older. I just don’t know what to do.. any advice?? No judgment please.