I don't want to loose their support as I do need it but I know they'd never support him again after this, which he needs to maintain a sober life, Right?
nope, he doesn't NEED their support or your support to stay sober. he needs to BE committed to staying sober no matter what, and that includes p!ssed off inlaws. i can see why they aren't grabbing the pom poms just yet.
he behaved atrociously.........over TIME. not just once. and while i'm sure there were honest reveals in the treatment session, he did NOT tell you EVERYTHING. there is always much, much more. they will reveal enough to get "atta boys" for telling the truth, and hope everyone just takes them at their word and doesn't look any deeper.
i'd say give it a year......and if in that time he has been able to maintain his recovery, keep up with meetings, after care, behave like a humble adult, not make demands on you.......then.......maybe you can talk about reconciling or re-cohabitating.