As they say, karma surely bites you one day. Tristan was feeling elated when Ava went against her parents and chose him, but now his daughter was doing the same thing. He was acting like a hypocrite.
Tristan knows Enzo wanted to marry Hazel as quickly as possible, but he feared Hazel's feelings may change, she may find someone better or she will realize she is not okay with their age gap. So he wants to trap her and close all the doors, giving her no choice but to love him.
A few years back, Tristan was also in the same boat, he married Ava as soon as she graduated so that she does not have any time to second guess their relationship.