You can focus on your H's OW and possibly go N/C with your H until he ends the A, WITH PROOF.
Or, you can, for all intents and purpose, understand that the A is a symptom which, even if the A ends, the problem will still remain. So this route means taking a look at your responsibility for the break down of your M, working on making yourself an even better person that you already are... that only a fool would leave... and hopefully your H will not be a fool.
Read Sandi2's "37 rules" stickied at the top of this part of the forum, for starters.
