I am 20 years old. My girlfriend and I have been together for a year. And because of strange circumstances we have been living together for nearly a year also. First couple months wee fine. But after that sex was super rare. I mean almost a month at a time before anything. She was in a relationship where I know she was more active and so was I. This is difficult and I feel like I am doing something wrong

You are, you are not talking to her,

1. if you were, most likely you would not have had the issue
2. if you had the issue you would know why
3. You would not be asking people who have no idea why, whyl
4. You would know that you and her need to sit down, when not upset, and calmly discuss this.

Stress, hormone changes, illness, work or money issues, all cause this.