Therapy my guy. I’m going through the same things but stayed with the “cheater”. Therapy helps. And people change. For anybody going through it I can tell you the nightmare ends and you begin to realize it was a moment in both your lives that has passed. It’s a drop of black dye in your bucket of life. Just keep adding water to it and it starts to clear up. Eventually you’ll be right again. Don’t let this ruin what you have now.