B and D are much the same and both are wrong. They shouldn't wave a banner proclaiming what they intend to do, but neither should their feelings for one another be hidden. If both share those feelings, there is no reason to go into hiding. The parents may actually give their approval for a deeper relationship sometime.
C is the precise reason for not doing either B or D. If there is not shared affection and commitment and mason is going to end the relationship because he's not getting what he wants, there is no secret to be kept. He's holding an ax over Alex's head, and it's the wrong answer.
A is the very first thing he needs to do. They share a relationship. Just what does Alex want to do? Does he care? He should. Anyone thinking about intimacy better find out if that's what the other person wants.