Should I not even say something like "How is the apartment seach going?" The last time we talked I told him to just let me know the availability of an apt he finds and we'll work out budget. I thought maybe mentioning something like that would tell him that I do validate and respect his decisions and I'm supporting them. I love searching anything (looking for a handyman, apartment, houses etc) but he, not so much.
Do you want to stay married or no? If you do, that's one decision I wouldn't support. You can still be respectful, but I wouldn't be helping him find a place, or move, or D unless that's what you want. Ideally, you want to stay in the same house as long as possible so he can start to see the new you and you want to postpone D as long as possible so he has time to work thru his own issues.