Just gonna rant about this a bit. Probably doesn't exactly apply to the OP, but may be helpful to others.
Jariel nails it, and to elaborate:
A lot of guys fall into the "nice guy" category by being afraid to go after what they want, driven by a fear of rejection.
Typically, they want a hot girl they know through their social circle. Instead of flirting/teasing, and then asking her out, they try to be nice to her, to become her friend. Maybe they flirt a little, but never aggressively try to seal the deal. This is all driven by the fear of rejection of a more direct approach. Their idea is that the girl will see what a "nice guy" they are and eventually develop feelings for him.
Instead, the girl can usually tell that the "nice guy" is into her, but is afraid to make a move. In other words, he appears weak and un-confident (not attractive). He holds her to a lower standard than he does his male peers. Things like flaking and being disrespectful are tolerated by the "nice guy" as he lets his oneitis walk all over him.
This situation usually ends up the guy using text message or other weak forms of communication (e-mail, via a friend, a letter) to proclaim his love, abruptly, when he can stand his blue balls no longer. Or after weeks/months of pretending to be friends, he makes a move and is rejected in a humiliating, excruciating ordeal.
The object of his affection recoils from this, expressing (and/or) feigning surprise that the "nice guy" has feelings for her. "I thought we were just friends", "I don't want to ruin our friendship", etc. Most girls won't want to lose his friendship (read: attention) at this point, and will happily string the "nice guy" along with little carrots of flirtation and attention.
Meanwhile, this "nice guy" will wonder why the world is so cruel, post messages and videos online wondering why girls like jerks, continue to pine for the girl, develop enormous blue-balls, and hopefully find SoSuave.
I put "nice guy" in quotes, because he isn't really a nice guy. He is, quite simply, a passive-aggressive, weak-willed, failure with women. His fear of rejection continues to prevent him from having the attitude and taking the chances that get desirable women to want him romantically.
I don't judge here. Many of us have been there, myself included. If you are recognizing this characteristic, you have taken an important step. Its better to go for what you want and fail honorably, than try to deceive a woman with a fake friendship to get what you want.
The best way to get over this is to pursue women. Really go after them. Be ****y/funny/whatever works for you. But don't try to be their friend. Try to isolate them and seduce them. If it doesn't work out in a short time period, then move on to someone else. Remember, if you have few or no options, an individual girl can become incredibly important in your mind. So cultivate a social life that allows you to interact with hot women regularly. Pursue your career and other goals to gain confidence in your general sense of purpose. Take care of your body and face. Dress well. Etc. You get the point.
