We do all have our ups and downs but for most of us things don't go horribly wrong. For many of us being poly works really well and makes for more authentic relationships. Your wife cheated and then tried to justify it, that's so far from what poly actually is. Poly is all about communication and consent and valuing the feelings and being gentle with all your partners. (and metamours)
Everything will be ok in the end. If it's not ok it's not the end.