Cheating isn't really ever okay.

With that being said, I would not ever condemn someone heck for it happening once. Sometimes heat of the moment things happen. The way to make up for that is to be completely open and honest with your partner and tell them what happened and let them make the decision (to stay together or break apart).

However, this isn't really heat of the moment. It's something you're kind of planning. Now believe me, I am not condemning you in any way. I am not calling you a bad person or anything, but morally it is something that you will regret. You're already questioning it. I think you'd be a much stronger person if you were able to not give in to the temptation.

Now, your first approach (if you decide not to give into this) would to be to figure out what the problem is with your husband. You may have to go to a marriage/sex counselor as well. After all, in a marriage not only do you have to make sacrifices but your partner as well. There's a reason that the intimate physical stuff isn't happening and you need to figure it out. You're already so frustrated that you're actually considering being intimate with someone else which isn't a good sign for this relationship.

So, first you need to figure out what's going on, then you need to decide if this marriage is right or not. If you two can never be intimate and you need that in your life then this may not be the right marriage for you and you two may be better going your separate ways.

Hope this helped some, and I wish you the best and hope you find the right path and take it.