boarder cross help info please

Hello, My name is Paul, im new to this boared, I have a problem that im taking very serious as it has to do with possably loosing my job and my american girlfriend at the same time. I have met an american girl 6 yrs ago on line, I have been dating this girl for 2.5 yrs now, I see her about once a month for one or two nights, I drive to see her as she cant drive far due to a bad back, I eather go see her on my way back from work in my truck as im a truck driver that goes through the states, or I see her with my own personal pickup truck, recently when crossing the boarder into the states I was asked to show proof that I wasnt going to live and work illigally in the states and stay with her, they ask for proof of work, and of my resedence, I live with my parents because I drive truck and im hardly around enough to make it worth while to buy a house, and both parents are older and need help so it works out good when im there, because of this reason, I dont pay the bills there under my name, and they wont let me because they write them off for tax reasons, so im having troubles proving to them that I live there, I even got parents to sighn a note stating I live there, nothing seams good enough for imagration, they have let me cross with my truck driving job so far, but keep asking for more proof, I had to cancel a trip into canada with her for christmas do to fear of not being able to get back into the states, even though shes an american citizen because I would be driving her, its a real shame after all these years of trust to get these questions now from them and fear that i will be turned down at some point and loose my job and my girlfriend, i hope someone can give me some advice or direction on this topic, I have givin them almost everything I have as proof, my drivers licence, passport, pay stubs, note of where i live, tax foarms, bank statement, and there asking me to keep all this in a beter folder for them.I have been nice and complient so far but I can only give so mutch proof, do I need to get married? please help if you can?

Paul