Well, return to being sweet and loving is a good start. Try again. Don't just leave her to hang with your friends too often (but you know, you should still be able to do that AND prove your love; they aren't mutually exclusive). If you "love her to death" why are you not trying? Reread your question and you can probably figure it out.
Ask yourself, If you're not making her happy and she doesn't want to hear your voice, identify what it is that you can change that she would prefer. You'll probably have to ask her if you don't already know. Then go do that, if you can. Then after doing what it is that she's missing, that you're capable of doing, check in again. "How do you feel now that I am. (whatever your doing)" Calling her on the phone more, going down on her in bed more, refraining from insulting her, whatever it was that was bugging her is now not bugging her, so that's called an improvement. Repeat this process until you run out of things that you are capable and willing to improve.
And if she wants something from you that you can't or don't want to do, well now you know. She's unhappy and she wants something from you that you cannot provide. Looks like you've got yourself a real issue to solve. Better talk to her about it; either she needs to change her wants because you can't comply. Or you need to change your capabilities in order to give her something more. Either way works. But ignoring a fundamental relationship issue DOESN'T work.