I think the father is meant to represent comfort, and in a sense arrested development. Andrew feels held back by his father, and it's suggested that he is embarrassed by his father's lack of accomplishment in life. The Gushers moment to me suggests that the father still treats Andrew like a kid when he desperately wants to be an adult, and only Fletcher treats him as such. You're right that the dad is always there for him, but Andrew's desire to break free of the nest leads to him feeling smothered and running back into the arms of an abuser. The last shot of the dad watching Andrew on stage reflects the tragic end of their relationship, as he knows that he has lost his son despite his best intentions.