I'm sorry your relationship is going through such a rough time.
if you both are agreeable to it-- I think couples therapy could perhaps help.

I think ANY kind of affair can be equally painful-- I don't think emotional or physical is more or less hurtful than the other.
either way it is-- a person going outside their current relationship to seek and get that which they crave/want-- without/or little regard to their partners feelings.

best to you

fins