Hi. It sounds like you're having a tough time of it! I'm guessing that neither one of you is mean or badly intentioned, but it sounds like both of you have needs that aren't getting met and you're having a really hard time figuring out what to do and how to do it.
The thing is, opening up a marriage is something that you do when your marriage is working well; and part of working well is running that relationship on honesty and trust. It sounds like the honesty and trust parts of your marriage are broken right now.
I know that you're needing to feel love and intimacy, and that it's really tempting to seek out those things elsewhere. I know that the short-term temptation can be really hard to resist, but I'm guessing that if you focus on your long-term benefit, you'll end up, honestly, happier.
So, the most selfish thing you can do right now, and also the best thing for you, is to put huge amounts of effort into fixing your marriage or ending your marriage. And, while you do that, you should, emphatically, not be seeing anybody else.
I suggest that you both stop dating other people and that you go to marriage counseling. If that doesn't work and you find that you can't trust your husband or yourself to treat each other respectfully and honestly, end things--despite the risk you face of losing the nice house and your comfortable life style. Finding a space where you feel at ease with your ethics and your forward-moving progress is much better than stagnating in semi-comfort with fundamental relationship problems.