I thought he lead her on or cheated on her. Something like that. It is one of the reasons my friends can't stand him now. I agree with you that Mark is very immature and insensitive sometimes. He acts like he should be treated different because he has won two seasons and some pros have not.I don't know what he did to Sabrina I started not liking him during his partnership with Kim Kardashian and later on with Melissa Joan Hart, because I thought he treated them like crap when they were eliminated, and he can't take the criticism very well. I'll give him that all the pros (for the most part) have had it out with not taking the criticism (I know Maks doesn't hold back and I love him for it), but I've felt Mark comes across as a spoiled 3 year old.
Which stinks because I really like Chelsea from the video footage I just watched of them together dancing.