You're not going to like this...
Get more girls
jajajajaja

Perfect answer Tyme, really.
DKD, you should do this and you won't care when girls don't turn to be your lovers.
The only thing I can tell you besides the great advice of Tyme that may give you some hope is to be honest (not in a direct way as in "I like you so much and want to be something more than just friends". That's death sentence for sure).
If you've been friends with her too long you should not do this because it doesn't make sense. If it's just a new girl, well, you could message her something like this:
Her: "We should watch a movie tomorrow"
You: "Great, but this time I won't behave around you"
Her: "What do you mean?"
You: "Lets just say I can't be a nice guy too long when I like a girl

"
Fuck it. Depending on her response you will know if she sort of gives you a go for this or not. If she doesn't just cut it. You stop texting her. Now she knows you mean business and if she contacts you, well, she knows what to expect. You can haver your chance.
Usually it won't work but at least there is a chance it might.
Cheers!