Maybe I'm a little older and more experienced than a lot of others in this thread.
There is something very important you have to remember about women at all times, especially if you're starting to have serious feelings for one.
Women aren't men. Women don't think like men. Men don't even think quite like one another. Don't think you understand her or know what she's going to do or what she feels, because you don't.
Women are especially good at sensing desperation. There are some suggestions from the field of evolutionary psychology that this is an ability they evolved to help them select appropriate mates. And some--not all, not most, but a significant number, and more than will admit it--get their jollies playing sadistic games with guys who seem desperate. Stringing you along, raising your hopes only to crush them, makes them horny. They get off on it. You will meet significant numbers of women like this. Always keep in mind the possibility that she's lying to you, especially if things seem too good to be true.
If you forget this, you're going to get hurt, very very badly. You're probably going to get hurt even if you remember it but forgetting it makes it certain that the pain is going to come early and often.
And you may find as the years go by that you worry about such things less and less anyway. Maybe at twenty you're a horndog and you can't stop thinking about sex. Spend ten years busting your ass working sixty hours a week and at thirty, you'll be able to take it or leave it, as you please. Women may or may not find you more attractive, you may or may not have more success with them, but it will matter less to you. By forty you won't give a shit: "fuck you, if you don't like me. I have a hobby and it's not you."
And that bitch who strung you along and lied to you and broke your heart so badly when you were twenty-three that you couldn't even bring yourself to date for ten years after that? She's broke now, living in a trailer with her four squalling projectile-vomiting brats, after she drove her husband away. You get to think about her and laugh now.
Like the man says, "You should listen to me 'cause my name is Charlie Mug and brudda, I been AROUND."