Give her what she wants. Leave her alone and go do things for yourself.
Go out and do whatever you want. Reconnect with old friends.
Do not wait around for her.
But out of left field she tells me that she wants a break to "find herself".
This was out of left field for you, not her. She has been thinking about this for a while. There are other reasons she is breaking-up with you besides "finding herself".
She insist that she love me and wants to spend the rest of her life with me. She says that I don't have to wait for her but she feels that we are going to be together in the future (however long that is).
She is trying to break it to you easy by instilling hope that something will happen between you in the future. Don't fall for that. If she really wanted to spend the rest of her life with you, she would not be doing this.
She has told you what she will be doing when she says "you don't have to wait for her". She is going to be moving on and you should be doing the same. DO NOT WAIT FOR HER.
Time to let go and start healing. It's going to be immensely difficult for a while, but in a few weeks, you will get better.
Sorry man, we all go through this at one point or another. Be happy that you two shared all of that time together. 3 years is a long time, many people don't even last 3 months.
That "promise ring" really doesn't mean anything now. It may have meant something before her feelings for you changed, but now it's just another piece of jewelry she will wear. I gave my ex a ring too. She still wears it, on her left hand no less, AND she is dating someone else... it's meaningless bro!