How do I over come the fear of my partner cheating on me?

I am in a relation-ship with a woman and she is the best woman that I have ever known very smart funny and loving ....I have been with her going on two years and we argue alot I always have this fear that she is doing me wrong and talking to other women ...Because she has in the past and lied to me several times before about doing this very thing and now she says that she isnt but I still feel like there is more to everything than what she is telling me I am younger than her. I need help but I feel as if we both need help in differnt areas. Like somtimes I feel as if she doesnt care cause I will be p[ouring my heart out to her and she wont even look at me ar talk back .. I ask her to be nice to me on several occations and still the looks and the smart comments .I love her so very much and I want to be with her I know that she loves me too but I just need some help on getting my best freind back I am here in this city where I am living 81\2 hours awys from all of my family and I dont know anybody here and I barley see her because she is always at work ....What can I do to improve my thinking and also my long relationship but most of all my cherished freind ship with her......PLease help me!!!!!!!!!!! Thank you I am open to any suggestions....My relationship is just like any other but what I am more focused on is saving my freindship with my best freind ...There are times I feel as if she has died and I diddent even get the chance to say my final good bye........Please dont critisize me for who I am and the life that I am tring to live because it feels good to me and it feels right so please help me....Thankyou SIncerly MEL...