ED / Reboot Advice

Hello, I am new here, came across this website about a week ago, so please excuse me if I don’t understand all the terms and abbreviations at the minute.

Ok so my problem is this, I have never had any problems with my penis until January last year, when I started to notice I couldn’t keep my erection when having sex with my girlfriend, which was frustrating as she was the hottest girl I’ve been with. I had never had any issues with the two girls I was with previously. Each time we had sex I could get an erection but then I’d lose it during. First forward to May of this year, I attempted to have sex with a girl again, we had been sexting and I was very turned on, I get to her place and it happens again. I’m not sure if this is porn addiction induced or death grip etc. Even when masturbating I have noticed my erection can come and go throughout. Starting off hard then going soft during but then becoming hard when ejaculating.
Would like some advice as I would like to get over this and have stronger firmer lasting erections for sex. Any advice would help. Cheers