I’ve liked the person in question for quite a while now, and I’m positive he’s realised. He calls me by a nickname, teases me and jokes around with me, and once said “I love you” to me after I helped him with something, albeit in a (probably) platonic way. But he should know better than to say something like that to someone he didn’t actually like, right? Especially since he knows that I probably like him, too, fully knowing the possibility that I might assume it’s in a romantic way? However, the catch is: his friends, some of my friends, and I know that he apparently likes someone else, and he doesn’t deny it when we ask him about it. Even so, I’ve never seen him talk to her, and his friends constantly tease us about how we should be together. I’m not sure if this is because he likes me, or if the fact that I like him is just somewhat obvious. Could the “liking that other girl” thing be a bluff? Or does he really like her and is just really oblivious to my feelings, around me? I don’t want to jump to any conclusions. I’m really not sure.
Thanks in advance for any help or advice!
LemonVibe 
[Steal him.
Try and get a date or something, make him see you’re interested and if he’s into it he’ll forget about the other girl.
If he’s not, well that’s just bad luck, but once you brush it off it won’t be so bad.
Make a move
[I’m going to guess by the situation that you’re in high school, or somewhere very close? That makes this a bit more difficult, due to the fact that high schoolers are assholes, plain and simple.
But let me give you an important life lesson… playing these games, trying to guess what he means when he says something, listening to what your friends think… these are all GIGANTIC wastes of your time. You don’t realize it now, but understanding yourself and what you want is far more important in the long run.
Ask him out. See what he says. Stop trying to interpret his every inflection, or acting on every conjecture… ask him, and then you’ll know. If he feels the same way, the other girl will probably fade into the background, as David said up there. If he doesn’t feel the same way, then you can pick yourself up, dust yourself off, and continue on with your life.
You have to know, or else you’re just wasting a MASSIVE amount of time and energy. Nothing is worth that.