Seems like Kourtney has been trying to control Scott's grieving process

...and it's backfiring. Considering the sequence of events I can't help seeing it that way. I think it scared Kourtney that Scott felt so lost and guilty because of both his parents passing away. Kourtney suggested the trip to the Hamptons because on some level she believed the trip would help make things better. That didn't work. I think she thought her pregnancy would help Scott. That compounded his anxiety.

It made Kourtney feel completely frustrated that things weren't going the way she wanted them to and she unfortunately took it out on him -- such as locking him out of the house, abandoning him and Khloe at the tennis court, etc. Then she even lectured Khloe for being a friend to Scott and having fun with him, because it didn't fit into Kourtney's plans.

Over the years Scott actually did make progress towards becoming a more mature, responsible adult. I think he felt that making his appearances would've been therapeutic for him and his family's situation. He may have been right about it being therapy for him, if not for having to fight for the right to attend them. Since Kourtney couldn't imagine his appearances being good for either of them and since they didn't coincide with her plans (to get Scott over his grief and guilt or whatever else), she chose to be unsupportive about them. When he got to make his paid appearances and to do other things in which he finally got a break from his family drama, he was feeling more rebellious than relieved, leading to one of the most dangerous nights of his life.

I'm sure Kourtney's heart was in the right place, but she's not a mental health expert. A mental health expert could tell her that she can't decide how someone's going to get over their grief and that it's a more uncertain process than that. Both Kourtney and Scott need counseling to give them better tools to deal with Scott's grief, to repair their relationship and to move past all this.