Sexual Fidelity is Absurd

Should I look in the mirror and feel self-loathing over the betrayal in which I engage? Because I don't. I simply no longer see the value in monogamy. As I see it we have a very short life, we are dead for a long time, and therefore I no longer have any interest in restraining myself to actions that are within the confining box of allowable behaviour.

So why am I in a place where I can keep these secrets and not feel bad about it? I don't want out of the marriage and I don't feel the need to confess my sins. I don't, in fact, see this as a "sin", for lack of a better term. Sexual fidelity seems profoundly ridiculous as a concept. It seems an outdated means of social control, a means of promoting a morality with which I do not agree. I recognize that this is perhaps a ridiculous justification, but I don't think my idea is wrong at the root.
After all, what is the purpose of sexual monogamy? If I am holding up my end of the relationship: helping in the house, being good to the kids, having dinner with the in-laws, spending time as a couple - what does a good toss in some sweaty sheets matter? If I am home at the end of the day when I am needed what harm does it do? Why is sole access to my sexuality considered a neccessary part of a relationship?

I don't think that I could go back at this point. Things are actually feeling better with the husband lately and I haven't even seen the adorable younger boyfriend in two months. He doesn't live here and we only get together when he is in town for work. But I love the idea of the whole thing. I love that I have a little something outside my life. And I think that when this ends, which I am confident it will - he is young and he will meet someone about whom he will become serious, at which point we will be over - of this I have no doubt. But when it ends - I think I will be on the lookout for someone else. In fact, I don't even know that I am opposed to someone else in the interim for that matter. I understand that this may indicate a pathology of some kind. I definitely now have an itch that requires a scratch - and even though things seem to be improving in my relationship - I still want to continue with the affair.