BEFORE this gets out of hand I'm going to jump in...
We tend to look down upon any kind of cheating, but we will still give advice. It can be tough to give up someone soley because of their looks. But it's one of those things that you may slap yourself later on if you decide to stay with her longer only to find out she cheated on you anyways or just breaks it off herself.
There are two main reasons people stay together in a potentially unhealthy relationship.....fea r of loss and hope for change. It may have reached a point that you two no longer love each other and stay together simply because you both don't want to be alone. You are both comfortable.
Once you reach a point that you are beginning to justify cheating then the relationship is already over, but you haven't accepted it yet.
She won't be the last "hot ass" you find. And if you want to be a true alpha that is non-needy then looks should be the second thing you worry about after her character. You will find another that is just as hot or hotter with a better personality.