i have two scenarios: one would be that he is one of his blood siblings that silas' birth mom kept (silas is adopted). and right now they are getting to know each other because silas recently found out that he knew his birth mother his whole life. it's something he is grappling with and having a hard time with. we can brainstorm this for sure.
the other scenario would be that he is someone that silas had a secret "thing" with. more than a fling, definitely feelings, but not just a hook up. it would be super complicated. also more brainstorming!