From my stance, not having a great relationship with my in-laws, I don't really see much to worry about it. Honestly, the only reason I have facebook at this point in my life is so I don't actually have to talk to my in-laws. I may be a horrible person, but there is very, very little my MIL can do that doesn't rub me the wrong way. We live over 1000 miles from both sets of parents, and I go out of my way to not talk to my MIL... If I see she's on caller id, I hand the phone to my husband. It's that bad. We joke that even my husband gets along better with my parents than his own. But with that in mind, my husband realizes my parents aren't perfect and can see their flaws. He can also see their flaws in me, just as I can see the influence of his parents in him. But that doesn't make us our parents, or our parents us. I don't believe that the way we interact with our in-laws, good or bad, is an extension of how we interact with our spouses. We interact with everyone as individuals. I think your struggle with your MIL is that you're feeling "facebook smothered." And honestly? I think that would annoy a lot of people.

I think the issue with your irritation with your husband which stems from your depression is another issue entirely. While I think you should ignore your MIL's clinging through facebook as much as you can (you realize it's irrational to get upset about it, so focus on not getting upset about it), I think you should pay attention to your depression. I think that is where Lee's concern stemmed from, and she was simply worried that that behavior could cause troubles for your marriage (I don't think the MIL issue will, especially since you two seem to be in agreement). I definitely understand the pain it is to constantly restart therapy, but you might want to look into it again, and yes, check their future moving plans before you start to really get into things. Personally, I think they should tell you as soon as they're considering or know if they're going to move to give you adequate time to transition away from them and to someone new.

Anyways, this is just my opinion. And remember, take it with a grain of salt.