Hi Danny
Well, I'm guessing that she does really like you, but perhaps not in a boyfriend / girlfriend way any more.
But it is only a guess.
You have known each other for a long time and you felt comfortable enough to ask her out, so perhaps you could actually ask her about her feelings.
I think that you need to accept, in advance, that there may only be friendship ahead, rather than romance, and, bearing this in mind, ask her exactly how she feels.
If she realises that you are willing to accept her true feelings, then she may feel able to tell you about them.
Teen romances can be confusing.
Being a teenager can be confusing anyway.
Don't let depression take over. If you do feel depressed, then talk to a school counsellor, or someone else who can talk things over with you.
Good luck!