2nd innings problem. This thing

Hello Dr, Recently i met my gf and when we got intimate, we did a lot of foreplays and then we had sex. The 1st round was very good, erection was proper, no looseness nothing. But when we try again after an hour, during penetration, the penis looses automatically! And looses hardness...(although my gfs V opening is small) Its happened with me for the 1st time and i am worried... and again after an hour we tried and the problem is same and it spoiled my mood too because penetration is not done. ( the day before we had sex, she also blowed me twice) Erection didn't happen like before and iam embarrassed... (yes i do watch porn and 4-5times masturbates in a week, and during porn and masturbation erection is proper)... i am overweight too.. 85kg and 5.5ft height. Please guide me what to do and why this happened... and how to overcome this thing🙏.