Performance Anxiety and Other Issues

i need help. over the course of the last two years i have developed really bad performance anxiety. ive been with my gf for two years and when we first started i was fine. however one day i was unable to perform and ever since then its been hit or miss. ever since that day i get really nervous and lately the only way i have been able to perform is if i have a few drinks to take the edge off. when we start kissing etc im literary thinking if i will get an erection and then when its time i lose it. i never had this problem until that one day but now i cant shake it. i use to be ready at a moments notice. we would do it in public places and now i cant act on the thoughts in my head. consequently this has made me shy away from sex and she thinks it is her. but if we start to do it and i cant perform she thinks it is her. i finally broke down and told her what was happening but she still thinks it is her. i will day dream at work about things i want to do with/to her but im terrified to try. what sucks is when im able to perform im really good, very attentive etc but again....its like i literally hear a voice telling me dont mess up
also my sex drive isnt where i like it. it never really has been but i think my other problem is making it lower

any thoughts etc would be appreciated..