I know a good deal about this, because I was going through the same issue with my now long term girlfriend. After stopping porn use and dialing back on masturbation, it took some time to become comfortable again in the bedroom, where I wasn't thinking about performance issues.

It's absolutely nothing to do with you. My girlfriend was and is super sexy to me and quickly makes me an 11/10 on the horny scale. The problem was that during sex I would start to worry about "What if I don't cum for some reason?" or "What if I can't stay hard?" and it would be a total mood killer. That thought created a viscous cycle, where I would start to have problems staying hard, or cumming, which would lead to more distracting thoughts, and thus continue the problem. Like you, my girlfriend also unhealthily tied my cumming to her happiness in the bedroom, which only made matters worse for me. Not only was I unable to perform for myself, but I was ruining her time too.

Communication was key for breaking the pattern. We sat down and talked several times over the course of a couple months (not during or right after sex, but when we were both relaxed), which helped change her mindset and taught her how to better react when I was experiencing performance issues, which removed the source of my stress. The best thing she started doing was to help me get back in the mood and show that it was ok for her and not affecting her fun. This hugely helped me build back my confidence, and prevented any distracting worries--since it was no longer a big deal if I couldn't cum or stay hard--and soon enough our problems were solved.

We now have awesome sex all the time, and even cum together sometimes, which is extra fun and bonding. It took good communication and both of our efforts to work through the problem. And time.