However your relationship started out-
This is the man he is today. A relationship isn't reform school. YOU can't do anything but stay out of his way as he tries to stop, and he doesn't want to stop.
You say you gave him an ultimatum around New Years, but you didn't really. It's March and you're still seeing him and waiting for him to call you. Your announcement meant nothing to him because you're still involved and dating him. You can continue if you like, that's your choice. Making threats won't change him. Making threats you don't follow through on won't change him.