Welcome to the collective. Give this a lot of thought. Here are some factors to consider while you are thinking about what to do:
1. Whatever you do, you don’t want to make the ring and the promise meaningless. So, if you decide to have sex with your boyfriend, take the ring off and renounce the promise. That way you are not lying to yourself and others.
2. Instead of worrying about this, ask your boyfriend what he is thinking. Also, tell him your decision in advance. Do not leave any doubts beforehand.
3. Long distance relationships almost never work. They have all the pressures of a normal relationship plus no shared experiences to help you grow and stay closer. I would think hard before breaking my promise for someone who is only in my life for a visit, and may be out of my life soon.
4. Relationships when you are young tend not to last long. Even first loves. Are you OK that if you have sex, you will likely end up breaking up with this guy anyway?
5. As casheroo said, alleno is full of it. Any guy who would not want to respect your promise or who would break up with you if you did not have sex with him is not worth being with anyway. He is also just as likely to break up with you when he gets tired of the sex.
Take your time. Think about what is right for you. Think beyond this visit to how you will feel in six months or a year.