Because of your decade away from real sex, your situation is no surprise. As you know, having sex with a partner is much different than masturbation with porn. Your body and mind will both have to adjust. With a supportive partner, you will heal. Naturally, with a new relationship, you want everything to go right, and some of that stress can make sex rather shaky at times. I recommend that you avoid masturbation and porn and enter into any sexual activities only with your partner so as to direct all your energies in that area to what is most important. Have plenty of foreplay without concentrating so much on orgasms; enjoy getting there, whether it's this time or next.
Welcome to age - tends to happen as you get older!! Sounds by what you said that you are still in fine form for a young man, don't worry, I don't think anything is wrong at all - I hope you really love and enjoy your new partner and her feelings for you are as intense and shared