Hi.
It's hard to know whether your boyfriend is gay or not without asking him. If you've heard rumors at school, they may be based on fact or they may be just the products of mean-spirited gossip. Do you have other indications? Is he not interested in kissing or having other intimate contact with you? Do you notice that he looks at guys a lot?
It sounds like it's really important for you to know for sure. If you do decide to ask, try to be non-judgmental about it. Also, be aware that he may not know exactly how to define his sexuality right now. Guys and girls often experiment at this age and many people move along the sexuality spectrum throughout their lifetimes--some taking wild leaps and others hardly budging at all.
In other words, be prepared to confront some potential gray areas. Think about whether you would still like to date him if he tells you that he's not sure about his sexual orientation. Think about whether you would still like to date him if he tells you that he's attracted to both girls and boys.
Your answer to these questions may depend on what's really important to you in this relationship. If exclusivity is key, then the thought of him being with anyone else might upset you too much; but if you're more concerned with the quality of time the two of you spend together, then you may be willing to be more accepting of his explorations--if he is exploring.
Take care.
