I'm sure there will be much deeper thoughts posted by others, but since I got online later than expected here are my quick thoughts based on one viewing...
My mother didn't like Stacy or Mark. Stacy because she took House's choice away from him and permanently damaged his leg. (To play devil's advocate I made the point that, hey, he could have died and while she should have respected his wishes, on an emotional level, you could understand why she did what she did. That fell on deaf ears. :/ ) And Mark because of his running a marathon comment to House when they first met. Was it nice? No. Was it human nature? Yes. Considering all the cheap shots House has taken at people (and received though barely registering them), I found it hard to get my back up. Plus, I could rationalize it was part of the mood swings. Unexpectedly meeting your wife's former love who she has obviously talked about quite a bit is going to up a healthy person's stress levels.
Though we're just scratching the surface with Stacy and her relationship with House, her presence has already given us the ability to see what he was like before The Leg. No surprise to me, he was much the same. :) The trauma House has experienced had to have changed him to a degree. The pain impacts how he lives his life on a daily basis. Then there was Wilson expressing his fears to Cameron a couple weeks back about House getting hurt again. After having his trust betrayed, it's going to be hard for him to open up again. But the House sarcasm, stubborness, determination, and single-mindedness? It takes a lifetime to build up those traits.
My assumption is Stacy left him and it wasn't due to the physical ailment. I don't believe House could get past his anger at her for not abiding by his wishes. The resentment festering in a relationship in which she already felt there wasn't room enough for her in his life. (I'd be interested to know if talk of marriage ever came up. She obviously isn't opposed to the idea. If so, is it something she put off because she knew she'd always take a backseat to his work?)
One of the things I love about the show is the small moments that can be incredibly telling. House's hypocricy is shown as he informs Stacy that he's going to abide by his patient's wishes, yet he's willing to drug the guy to get him in the clinic for tests. We have the humorous references to House's penchent for breaking the rules - "Property of OB GYN - Do Not Remove" as well as Stacy leaving cookies for the minions she knew would be sent to illegally search her home. Lest we forget Chase's betrayal, we have House's comment about the Aussie running if things turn rough. And how many people caught that House jammed the needle into Mark's thigh in the exact same place as he did to himself? Not so subtle Greg.
And here's where I get the rotten produce thrown at me ;) - I felt really bad for Cameron. There may have even been some dampening of the eyes. Shut up. Sure, her original approach to a relationship with House was jeuvenile, but her feelings nevertheless were real. Upon seeing him interact with Stacy, her excuse of 'he's screwed up that's why he can't love' is stripped away and the subsequent realization of "you just couldn't love me" has to be a huge blow. Now, after having her fantasy destroyed, is when she reveals some maturity - she seems genuinely happy that he has the ability to love someone even if it's not her.
OK, I'm out of coherent thoughts for the time being. Right now, I'm looking forward to Sela/Stacy's return because I want to see more layers pulled back. I just better not see House/Cameron/Stacy/Mark relationship drama take center stage. I get enough of that crap on my other shows.