Sean has supervised visitation because of a drug problem, you had to pay attention as they glossed over this on the show. It is on the slides if you need to confirm the fact. Anybody who has known a drug addict would understand that living with one is no picnic.
Yes, Kristy is resentful, probably after many years of living with Sean and the messes he created. She had to take the mother role to keep their lives afloat, and she seems to be still trying to teach Sean to be a man and take care of his children.
Possibly Kristy moved 2,000 miles away to be closer to family who could help her raise her children. Think of what they have gone through with his drug problems. Possibly she moved 2,000 miles away to earn more money.
Sean's remark about being tired of hearing Kristy is a single mom was just nasty. She's been a single mom all along, she has the toughest and most important job in the world. She needs to accept Sean for what he is, to put his misery behind her and be happy.
