Originally Posted by CielDuMatin
Maybe you need to distinguish friendship from romantic interest. I have quite a few people who I feel attracted to who are not available. But I know that and I don't let it go further in my mind than "wow, that person is attractive". I don't picture myself having a romantic relationship with them and certainly would never dream of acting on it in any way that made their lives difficult or ruined our friendship. (For the record, one of my friends does know that I find her very attractive in many ways, and the only reason I told her was because I knew I could trust her not to assume that that meant anything other than the fact that I think she is a dear sweet person...)
So there's nothing wrong with being attracted to someone, it's all about what you do with that, both your actions, and how much you let it eat at you.
Everyone has given great advice, but this
is exactly what I wanted to say. People say you can't help who you fall in love with, and to a certain extent that is true, but as soon as you realize you have feelings deeper than friendship you need to take action. If it is someone unavailable (monogamous, poly saturated, or whatever the situation may be), you need to stop your thought pattern. You can't focus on how he/she is great because of x,y, and z and "oh, my.. We would make such a perfect couple." You have to focus on the fact that you're friends, he/she is NOT available for anything more than what you're getting now, and that you don't want to risk causing yourself or anybody else pain by building unrealistic dreams/expectations.
I always think of it kind of like anger. It's not always appropriate to show anger. If I get pissed at my boss because he did something that I didn't like, I can't yell at him. I have to find some other way of getting that emotion out - going home and writing in a journal or writing a letter to him I'll never send or going to the gym or punching a pillow. If I get a crush or fall for someone that I know I can't have, I train myself to think of the positives of keeping the relationship the same and lavish the other people in my life with extra attention until I don't feel the need to act on anything with that particular person.
Opal also has an extremely good point. You need to figure out why you keep falling for unavailable people. After you figure that out, you should be able to figure out whether or not you truly need to stop getting close to people who aren't available for something more than a close friendship.