I Am In A Situation Where I Have Been Dating To Same Girl For Four Years. She Has Recenley Started Making Comments Such As "go Ahead But Dont Go Cheat On Me" And Also Has Been Asking Me If I Flirt With Other Girls When She Is Not Around. I Have Never Thought About Cheating On Her And I Don't Know What I Have Done To Put These Kind Of Thoughts In Her Head. She Says That When We Get Around Other People That Im Seem Much More Happy. It Is Not The People It Is Just That We Are Getting To Go Out And Have Fun. I Am A Funny Guy And She Always Thinks I Am Trying To Impress Other Females. I Try To Be The Best Man I Can Be To Her I Pay All Of The Bills I Surprise Her At Work With Flowers And Gifts And I Feal Like I Am An All Around Good Boyfriend. Why Is She Treting Me Like I Am A Womenizer?

Any Comments Will Help Thanks For Taking Your Time To Listen To Me.

From what I can tell she is insecure and feeling inadequate so she is putting it on you. I think she expects you to do something wrong and doesn't feel good enough about herself to not worry about it. There is nothing you can do to change it, only the way you respond to her. You can only reassure someone so much. Is she very needy and clingy also? OR is it just that she questions you being faithful?

Don't act sooo excited every time you go out. Mabe that'll help

She is definitely insecure and there is nothing you can really do to change her being like that.
Only time and her seeing that she should be grateful to have you so much that she doesn't want to lose you over her insecurity.
The only thing you can do is keep being yourself and loving her and don't give her any reason to think you ARE cheating on her. Like don't disappear for hours with no explanation. Eventually she should realize, "When does he have the time to cheat on me?"
Eventually she should realize you are basically the type of guy that is the life of the party and don't mean anything the way she seems to take it.
You could even maybe have a conversation with each other about your and her values and morals. That is one of the biggest mistakes people make nowadays they jump into a relationship and have no idea of who each other really are. They end up getting married and/or pregnant and then find out the guy doesn't want any kids and the girl wants to work and he wants her to stay home. She wants to live in the suburbs, he wants to live in the city, etc... It is better to have all the long talks about what you want in life and who you are before. Try having all these kind of talks with her so she actually sees you have long term serious on your mind to ease hers.

Maybe she cheated before and now she's scare that you may do the same... my friends right next to me told me that when you cheat you feel insecure of the other person(personal experience)... don't take it personal the (experience)

No offence but why did you capitalize the first letter of every word?
But just reassure her MORE. My boyfriend is great but he could do more. :/