How to be subtle about making a character gay?

I know I should've posted this on r/writing but I just didn't feel comfortable posting this there. I myself, am not gay but I am writing a novel and I have an urge to dive more into my characters and their personality and such. I don't want to blatantly have my character look at another characters ass and such but i just want to be subtle about it. Are there any signs where I can make a character a closeted gay without it being too obvious?