To catch you up to speed (although you should be in the know, since there are SPOILERS): In Episode 3, we got an intimate look at Cal’s adolescence and his friends-to-lovers arc with his best friend Derek. After their romance fully blossomed — culminating in a touching first night out at a gay bar in the outskirts of town — Cal finds out his girlfriend, Marsha, is pregnant. As a result, he leaves Derek behind and settles down with Marsha to start a family. Cut to the man we know today: An abusive, overbearing, resentful father.
Source: https://www.buzzfeed.com/natalieoganesyan/eric-dane-euphoria-nude-monologue-prosthetic-episode-4