Am I gay if I get hard looking at naked men at the public gym showers?

Yes. No. No one can tell you that but you. Do you find men physically attractive? Does the idea of a relationship with a man make you happy? You'll know in good time if you are gay, straight, bisexual, bicurious, whatever...

Do you want to have sex with them, If so you may be, or at least bi sexual.

If this man makes you want to explore him further why not find another gay man and see how things go. It doesn't matter if you are gay or not. Do what makes u happy.

How old are you? It may just be a natural reaction to being naked around someone else. When your young most guys don't have a lot of control over it. As you get older you will have more control. I would say if you are already older then you have to ask yourself WHY are you getting excited. Do you think about sex with him? If not maybe you just like the feeling of being naked around other guys. You might try a nudist camp. Sexuality is a very complicated issue.