I totally agree with the other posters here. Counseling would be very helpful.

However, I do want to provide a second perspective. Living in fairly liberal places, I know people (myself included) who are or used to be in "swinging" relationships, others in open relationships... this works for some couples well. Celebrities like Dolly Parton and Sting partake in this. One can argue both ways when it comes to polyamory vs monogamy, but both (all) parties need to honestly discuss and embrace whichever the partnership has agreed upon, even if it changes.

Note that you know your husband most, and the fact that he's lied in the past about other things does not bode well on his part. Worse, that he's shrugging it off... is he embarrassed? Or does he want to avoid an argument? Or does he not care to discuss the topic with you?

There are many reasons why people would cheat. Sometimes it's due to the relationship. Other times it's due to the fact that it makes them feel good about themselves, even though they are hurting the person they should be caring about most. I never understood it, and I don't think I will.

I'm sorry you are going through this, and many hugs. Looks like you have a strong plan in mind.