Feeling discouraged but hopeful

Ive been using since I was 13 (27 now) longest Ive been clean is one month. Clean for a little over a week now. Last night me and my girlfriend were getting intimate and I just couldnt stay hard. Im feeling discouraged because of that. The last week has been a struggle to say the least and I thought that being intimate with her would help. I did stay rock hard sometimes, but then inevitably I would go soft. The mental game is so tough. Any words of encouragement would be so helpful. Thanks all.