It's not easy when the kids are at these ages, I won't kid you. And being housebound is not always pleasant. I've been in that scenario when mine were those ages. When my youngest began preschool, which came about from early intervention due to a speech delay at the doctor's request and school district assessment, I was able to arrange a sitter for an hour to see my kids onto their school buses and I found a part time position with mother's hours. Being around other adults and getting back to work helped me to overcome the isolation that I felt. This school year, I've found myself in a promoted position, unofficially the assistant to the director of the division that I work for. My hours are still mother's hours in a unique way though it's full time due to working within a school system. My sons are now 10(turning 11 soon), 12 and 14.
I'm also actively involved with the PTA in my sons school district.
It would seem important to talk to your husband about how you are feeling, if he's open to such a conversation. And maybe a risk assessment for depression with your doctor? You're still within that first year of giving birth. Could be situational, of course.
And if your husband isn't a supportive partner, then it's important to make a mental note of that as well. Having a bigger brood, as I refer to my own, is as stated in my last post, life altering. Is your husband also feeling the overwhelming weight of the responsibilities? Could that be why he seems to have lost his own spark with you?
There's nothing wrong with having entertained the thought of another man. We're only human. It speaks volumes of your character to not have acted upon anything, it would truly complicate things, not that in these circumstances it couldn't potentially be forgiven with all you are going through provided it were a whim.