From what I can tell, there are two things going on here. The first has to do with your addiction. I’m not a specialist in that area, and I don’t even know to what you are addicted, but the fact that it took you eight months to start having sex tells me that whatever it is you’re addicted to is having an negative effect on your libido. So that’s one aspect of all this. But with or without an addiction, if someone fears that they’re going to have a problem in the bedroom, such as having an erection, then that fear will come true. So between the two effects, it’s not surprising that you are having such problems.

The first thing I would advise you to do is show your girlfriend my answer. You’re right, this is not her “fault” and so she shouldn’t feel badly about it. Maybe, if your doctor can help you kick your addiction, this problem will resolve itself. And with her help and a little patience, the two of you could probably beat the problem of your fears coming true. I’m not sure that you can beat both effects at the same time, however, so maybe your sex life is going to have to be put on the back burner for a while, assuming she’s willing to put up with that.