I can sort of empathize with your situation. However, it is different for me. I too feel like I need to tell the ones close to me the things that are troubling for me, but it is actually a relief for me.
I can't pretend to know exactly what you are going through, but like jcook144 said, you are not alone. You have taken an important step in coming on here and reaching out to us and asking for help. There is no instant cure, but it can get easier. We are all here for you.
Maybe instead of telling your girlfriend everything, you write it all here for us to read. (Personal details could be changed.) That way you could maybe make a transitition of not having that urge to tell her everything. I am not a doctor, I am simply someone who also suffers from OCD, so please don't take this advice from a medical standpoint.
Good luck.
I feel the same way as you. It started with severe anxiety and now has expanded to depression. Its a helpless feeling. I am also in a relationship with my boyfriend for over a year and it can be tough. I tell him all my thoughts but no matter how hard he tries he just cant fully understand what im feeling. He tells me that there is hope and life is worth living and maybe i know that on the surface but deep down my mind just tells me that im trapped and theres no getting out. I have a lot of suicidal thoughts and i feel like ive completly lost myself. Trust me, I know what you feel. Im taking lexapro which is suposed to help anxiety and depression and it does a little, but not fully. I know that venting how you feel can help a lot. I vent all my emotions to my boyfriend and cry and sometimes i feel embarassed but in the end it always makes me feel better. If you feel on the verge of crying, my advice would be to just let it all out...it gets a lot off your chest. Other than that, i have yet to find a cure for my feelings. Just letting you know your not alone.