It is not unusual for addicts new to rehab to want to come home within the first week or two. Most stay and are glad they did, some do not. The thing is, they are not locked in and have the choice to leave any time. Or they can get themselves thrown out with bad behaviour or breaking the rules, even if they don't use.
What I am trying to say is that this rehab visit will be as successful or unsuccessful as his willingness to to find recovery and you are doing the best thing by just stepping back and not participating in the chaos and instead, finding meetings for yourself and working on your own issues.
As for your parents, what about a brief visit to see them. It strikes me that it would not be uncommon for you to get them to your place and then have your roommate/partner show up at the door and cause problems. Going to visit them would get you away for a while and ensure that no drama would throw your world into chaos.
I really hope this all ends well for you and your partner, but please prepare yourself to deal with whichever way it goes.
Hugs