What's wrong with me?

Hello everyone! It is my first post here and, if possible, would like to receive your advice or suggestion about this problem. In a relationship with a girl for several years. Our sex was totally fine, but not regular due to ous tough study/work time, sometimes 2 times a month, rarely 2 times every week, between it I fapped almost every day, not extreme porn, just for 5-10 maximum. Something like a month ago we had an issue, that right before penetration or at the beginning of it I lose my erection, but during foreplay or her head/hand, its full erection and she can easily blow me. After 2 or 3 times like it, we could have proper sex, but it takes a longer foreplay time for me and concentration only on her, not my erection. It might be worried about previous *fail, kind of loop in your minds. Last time I worried about it again and we just decided to give oral pleasure to each one. Had anyone experience with such a problem? Possible problems are too much porn and masturbation (stop it already almost for a week), performance anxiety?