Infidelity happens for plenty of reasons. None of them good ones. It happens because of ego or stupidity or breakage. Or because of smugness or ignorance or a widening ache or an emptiness or the need to know 'what else is there'. It happens because of arrogance or a lack of self-control or because of that thing in all of us that wants to feel adored or heroic or important or powerful or as though we matter. It happens because there's a moment when the opportunity for this to happen is wide open and full of aliveness and temptation and it's exciting and it's there and it acts like it can keep a secret and as though it won't' do any damage at all.