Listen I know there’s meta about my sad garbage husband and his trust issues and how Kate is the first person besides his brother he opens up to and so on, but I still have feelings about this.
Seth had stuck with Richie out of necessity their whole lives as partners. He didn’t pick his brother, but his brother didn’t pick him either. Vanessa and Sonja both told Seth they were his partner, made that choice for him. Sure he chose to marry Vanessa and he chose to get Sonja involved, but he didn’t fully see either of them as partners, not how he did his brother. They were just tagalongs. Casualties. But Kate… Kate, who he spent ONLY THREE MONTHS with, who was just a damn kid, who took care of his strung out ass, who lost everything to the same fucked up shit that took his brother… Those three months were all it took for Seth to look at Kate and decide for himself, for the first time that we’ve ever seen, that this person could make a good partner. She asked him, but didn’t demand it. She wanted to prove herself, but didn’t claim any right to it. The trouble was he knew they were each on their own dark path. They couldn’t work as a team, no matter how much they each wanted to, while they were consumed with their own agendas. When he hears about what happened to her, and in passing, it destroys him. You can see it in his reaction. The first person he ever chose to be his partner, the first person to care about him despite being a colossal fuck up, is gone. Just like that.