If he really cared about her he would have long since released her to the care of her family and gone on with his life. His demand to have it HIS way, at all costs, is the most telling of both his motives and his character IMHO.
Well, he has been called a controlling person...besides being spiteful. If Terri did indeed have an eating disorder, I believe that Michael may have been at the bottom of it. Since he is so controlling, it's quite possible that he hounded her relentlessly about her weight.