The question I have is: do I just do nothing. Say nothing further until he brings it up. Ride it out a little longer. See if his actions continue to move forward and ignore his words.
Or do I initiate saying my boundaries. I can say I will not make a decision for him.
Next option is: you should leave. You don't want a M.
HaWho ... as apposed to what? You can not control him nor what he does .. .and going after him and pressing him on the issue will only add to him reacting as MLCr's do with pressure. As far as his actions .. 'Believe nothing of what they say and 50% of what they do' ring a bell?
A boundary of "I will not make your decision for you" is not a boundary as it does not protect YOU ... if he asks you "I am thinking of getting an apt what do you think" a reply could easily be "That's a decision you will have to make on your own" and leave it at that.
Read up on BOUNDARIES
"You should Leave, You Don't Want a M" <--- to me .. while that may be how you feel ... it comes across as an ultimatum, now is this is what you want ... your H to leave? I would change that last part to "I feel you don't want this M" but you may prepare yourself for some spew and things you may not want to hear ... IMHO