Please help me. I don't know what to do. It's hard to explain. I am not gay because I know I am not, but why do I get a get a boner from a guy on TV or movie in underwear? I sometimes get a boner from a girl, but I know in my mind I am not gay. Is my penis going to stop getting boners from a guy? Can you control it? Help! This is really awkward to write about!
You are not gay because you have not engaged in sex with another guy and you have no logical desire to do so. So calm down on that point. You're a perfectly normal healthy guy.
Once your body gains the ability to have erections, they are very difficult to control early on. Erections are new and your brain is trying to learn when is the proper time to have them. At first, it triggers an erection almost at random. As a result, they are often called spontaneous erections because they happen at seemingly arbitrary times. For the most part, becoming a man means learning to live with the reactions of a man's body, which includes erections. Your response to these erections helps the brain narrow down when erections are appropriate. When they come at the wrong time and you are embarrassed by it, your brain begins to learn that certain situations are not the best time to get erect.
The primary trigger for erections is sexual ideas. Most of us grow up keeping our bodies private, but seeing another guy in little or no clothing has sexual connotations, which is why producers put such scenes in movies. Even though you have no sexual desire for other boys or men, the situation is enough for your developing and oversensitive mind to trigger an erection. It is too easy to imagine yourself in a similar situation and you know how your body would react in such a situation -- and then it does. All too often you know the reason a guy is in his underwear is because he is about to take it off to have sex, even if the actual sex is not shown, that then triggers a sexual response in you.
As you get older, you slowly learn how to keep yourself from getting tense and to distract your mind from sexual ideas. It won't stop all erections when you don't want them, but it will help to decrease them. Limiting erections comes with practice. There is a feedback loop where the brain triggers an erection, but the erection starts the brain thinking about sexy situations, which then strengthens the erection. Most guys eventually learn to distract themselves when they feel an erection coming on at a bad time. Start solving a math problem in your head and the erection will quickly fade because you have broken the cycle.
Sadly those who are trying to make homosexuality acceptable tell boys that having erections around other guys means they are gay. It has absolutely nothing to do with homosexuality. It is simply a phase all guys go through as their bodies learn when to respond and not respond to various situations. But you can see how not knowing what is going on can plant seeds of doubt in a guy's mind and for some lead them to choose homosexuality even through their bodies are not designed to have sex with other guys.