IF a man likes to behold other "handsome " guys " is he gay ?

I would say that if you find other men sexually arousing, then the answer might be yes. I was married to an artist who found men attractive but it didn't turn him on. He just appreciated the beauty from an artist point of view.

If you find both men and women attractive in a sexual way then you may be bisexual.

Everyone goes through experimental phases whether they act on them or not. It is quite normal to "try on" different ways of being just to see if they fit. That includes everything from pretending to be a baseball player when you are 4 to thinking about sex when you are older.

Only you can say in the end if you are gay or Bi or straight.

if you want to have sex with them, then he is gay.
thinking another man is handsome is normal