Their last day inside Nemesis was still carved in their memories. No matter how much time passed, both Clay and Rick would always remember in detail as if it happened in the previous day. Maybe it was the trauma that they got.
The person that got affected the most by that event was Clay. He didn't only remember and dream about that day, but felt everything, each sensation. That was, after all, the first big loss that he had in his life, and the day when he nearly lost his family, the only family that didn't seem fake at all.
He never thought before that he could hold such feelings towards someone just like he did with Rick. That was why he always claimed that Rick was part of his family, and this time was different from the other ones that he had in the past. It had more meaning to it than just surviving.