I am in a relationship for 2 years but I feel attracted towards this guy, he makes me very nervous every time I see him, I love my boyfriend and I feel so bad that this other guy makes me feel this way, has this happened to you? why does this happen?

Yes its somewhat normal.
Ive been with my girlfriend for a while now, and visually see other girls who are attractive, if I'm walking down the street or whatever. Doesn't mean I go around checking them out or anything like that - its normal to think someone looks all right even if your with someone else.

Its when you act on it, is the problem.

At the end of the day what you have with your boyfriend is far more deep than what you may have with that other guy.

I went through the same thing. Whenever I was around this person, I couldn't speak intelligible sentences. I would get so nervous that evening saying "HI" was difficult. The cool thing was this person didn't have the same problem. And now we live together!! So sometimes it does work out for the best.

But you are in a relationship and that is the difficult part.

Its more than normal, its human and we humans are very capable of being attracted to, or liking many others besides our current love.

You cannot control what you feel for others, but you can control what you do about those feelings, and make a choice to NOT cross the lines of good behavior.

It's normal. You can be attracted to someone else even when in a relationship. What you need to worry about is acting on it.