It was subtle early on, but then Carlos beats himself up over it when Elliot wakes up. (The prologue of ZAGS is taken word-for-word from Carlos' coming out in the hospital in YAGS.)
I guess you may not have seen that scene in YAGS if you were always close to Carlos (and he therefore came out to you earlier in the game), since in this case his crush on Elliot is mostly replaced by one on you, instead.
(He considers you "safer" because it wouldn't involve having to come out at the frat. It's the same reason Elliot is off with Dan, segmenting that part of his life away from the frat house.)
