I have been dating my girlfriend for 3.5 years the other night I met up with her to talk and she told me she wanted a break... I asked her about seeing other people and she said I should go out and meet new people because I am reserved and stuff and I asked her about having sex with other people and she said its OK as long as it is with no one she knows and as along as I don't tell her... to whole time she was crying and she told me she loves me and kept on kissing me I am 22 she is 19 soon to be 20 I also told her I see myself marrying her and she said she sees this too she just thinks that recently I have not been showing her as much love as I should and that she doesn't want to lose all her love for me so this break will show her whether I am what she wants.. I don't understand this if she really loves me wouldn't she want to work through this together with me? I am not sure what to do I don't want to lose her but I don't want to wait and then be destroyed knowing she is never coming back any advice?

It was what she said, that you didn't show her love or paid enough attention to her. She has lost feelings for you and these kind of breaks usually lead to break-ups, believe me I have been there. You are young and also people change a lot during those years, maybe you have grown apart.
I recommend not bothering her at all in the meanwhile and hanging out with friends and family and doing fun stuff and trying new things. I am not going to say it will make you feel great but it will make you feel better than sitting at home thinking about the situation.
Remember, what ever happens don't perceive it as good or bad, its just how we see things. Behind everything is a greater good. New situations arise when old ones break down, everything is a cycle, life has its ups and downs.