dude , you in a spot man , i had almost the very same thing happen to me many years ago with my first wife only i was the one in the dark my brother knew about all the stuff that was going on aand didnt tell me cause he was in the same boat as you are this moment , almost to the day that the stuff was gonna hit the fan he finally told me what was going on and dont think i need to tell you how brothers settle things as you more than likely already know ,, long crappy story short the wife split anyway (and good riddence) but i didnt talk to my brother for about 5 years that i will never get back ..

hes your brother , tell him ...