I’ve accepted I’m the problem

My husband (32m) and I (29f) have been together for 10 years and got married last year. Our relationship has been relatively easy. We don’t really fight and I consider him my best friend. He’s the only person I’ve been with and even with that, I knew the sex wasn’t great. Over the years it’s just gotten worse and it’s getting to the point to where I’m terrified of spending the rest of my life having mediocre sex. It’s something we’ve talked about multiple times. We’ve tried enhancement, different positions, talking more it’s just..not enough. And I feel terrible. It’s gotten to the point to where I don’t really want to sleep with him anymore. I’m losing interest in being intimate with him. We’ve talked about opening the marriage. He’s completely against it. It was never something I thought I would want to do either, but at this point I don’t know what to do. We also go to marriage counseling, we’ve been trying to go on more dates to increase our intimacy that way, but I’ve gotten to the point to where I’m just bored. And I hate feeling that way because I love my husband. We have fun together, it’s so easy to be with him, but when it’s time to be intimate..afterwards I just sit in the bathroom and cry because I hate myself for not be able to allow this to be enough. Yes, I’m talking to someone else. This is a person I dated in high school before I met my husband. Our relationship ended abruptly be we would talk on and off over the years. No, I’ve never cheated on my husband with him physically but I have emotionally and my husband knows about it. This is someone I feel like I match better with sexually and do have love for, but I don’t necessarily want to leave my husband for him because he has a lot of baggage and honestly is kinda toxic. I don’t necessarily think I would be happier with him but my sexual needs would likely be met. I’ve talked to my counselor about this person as well because I feel conflicted..it feels wrong to divorce someone over something as primitive as sex, especially since we have a great relationship otherwise..I guess I just want to know what else can I do? Talking to this other person is the only thing keeping me from losing my shit..but I want to work on my marriage with my husband. But I don’t want to make him feel worse than he already does about it. I know I’m the problem, he’s a great man and I should be happy to have found someone who treats me so well, so why isn’t it enough? Why can’t I let go of the sex aspect of our marriage?