You have to remember, despite what the popular culture might tell you, that no one can know if another person is gay unless they come out and say so. That being said, it’s always worth keeping your eye out for any possible clues. Here are a few to watch for.
Does he show affection to men? If he’s showing affection to men, even if it’s just a handshake or hug, it could be a sign that he’s gay. This is because gay people tend to have a more fluid sexual orientation than their heterosexual counterparts.
Is he ogling other men? This is a big red flag, and not one to be ignored. It’s important to note that ogling doesn’t have to be physical – it can also be an unspoken attraction that manifests as non-verbal body language, such as a lingering gaze or a man-to-man hug that feels weird and unsettling.
Do you notice him hanging out in groups of guys and spending time with them when he’s not with you? This is a clear indication that he’s more into men than women. This is because men who are gay (and bisexuals and pansexuals) tend to hang out with other men rather than girls.
Does he mention his friends who are gay? While he might be joking around, it’s still an important indicator that he’s gay. This is especially true if his friends are openly gay or at least closeted homosexuals.