Guilt is your brain's way of telling you that you're, you know, actually doing something wrong.
Either quit this clear 100% express train to a sexual affair and work on your marriage, or end your marriage. You're being incredibly unfair to your husband. He's entitled to someone who's committed to him, and so is your pal's wife.
And it's really telling that he didn't feel bad until she started doing whatever for him -- as if his affection for her hinges on whether she does the wash. Consider what a prize he must be if his loyalty depends on clean socks.
Affairs are nasty, selfish, and hurtful. Your husband will find out, and so will your pal's wife. And if you have kids, they will figure out something is up, too.
You can really ruin your life. We have seen a lot of people come and go through here who really ruined their lives (sometimes through leaked texts or pictures, by the way), or they're the betrayed spouse and are devastated. And we've seen former other men and women -- and a lot of them aren't happy, either.
Suppressing guilt is only delaying the inevitable. Guilt is the little voice in your head. It's a mistake to ignore it and squash it.