So sorry for the pain you are in. You are dealing with much more than your garden variety infidelity. MB is a valuable place for that, but unfortunately you are dealing with a horse of a very different color. Please please please visit
Recovery Nation ASAP.
You can find massive help there in three different areas; for you as a partner, your H, if he chooses, and eventually for couples who make it to recovery.
Even if he doesn't choose this route, you will find excellent free support in the partner's area from coaches and a all-too-large community of people dealing with the fallout of their partner's compulsive sexual behavior.