I think you're the real idiot for believing that a guest star's relationship with a main character is endgame. Besides, they broke up and will probably never get back together. Lou returning to the show is a complete mystery.
https://www.tumblr.com/sherlocking-out-loud/790762790386286592/i-cant-assume-anything-happened-that-we-didnt?source=share
errrr.. are you aware that the show is one main character down at the moment? and are you aware that recurring cast can become regular? and are you aware that a recurring character becoming a long term love interest (endgame or not) by marrying a main character is a very good reason to promote it to regular? are you aware this is something that happens in shows in general, and abc's shows are not an exception? so yeah, it's perfectly possible for Buck and Tommy to get married and for Lou to be bumped up from a recurring role, I'm glad you agree.
Tommy is a firefighter, he was a part of the 118 so he knows everyone, he saved Bobby's life (more than once), and Eddie's life and Chim's life - which means that the 118 would not exist as it is today without him - he's a helicopter pilot (which is an interesting skill to have on a first responder procedural), he's interesting - he was in the military, he was closeted, he doesn't have a relationship with his father (why? is it because he's gay or there's more to it? what happened to his mother?), he's insecure (why? family trauma? relationship trauma? what in his past made him like this?). and besides ALL of this..... he's in love with Buck and Buck is in love with him. so yeah, there are a lot of good reasons for them to get back together.
meanwhile Buck has stated - ON SCREEN - that he's not in love with Eddie and Eddie has said - ON SCREEN - that he's straight.
who's the idiot again, anon?.....