I wouldn't ask or hear any response. If you promise fidelity either deliver it or pack your bags. Otherwise, be honorable and don't make promises you won't keep. You could ask for an open relationship. You could move on. You could ask for therapy. You could work on whatever problems are going on in your head or in the relationship that are leading you toward cheating.

Out of all the possible xourses of action before the actual cheating takes place..... If you didn't bother with any of those, why the fuck would I give a rat's ass about why you did what you did after the fact? What does it serve? It won't change my response one little bit.