I've done it all my life that I can remember
'Anon', your man has probably been doing it all his life too. I really enjoy exposing myself to young women while I'm jacking off. I do have web sites that I use too, but nothing beats the real thing. Having a young women, that is a complete stranger, walk up to your car and catch you jacking off is so exciting, especially if she sees you cum.
If you really like the guy don't find fault in what he likes to do. You might think about joining him. Tell him you want to watch him jackoff while looking at young girls on the computer. You have to stay fully clothed. That adds to the excitment. There will be great sex to cum later. After you do this a few time you can get naked too and masturbate while you watch him. I know he will be impressed and want to enjoy you more and more.
There was this one woman that I dated for a long time that I would let her see my cock sticking out of my shorts. She would take long looks. I even did it in front of a couple of her friends. She would tell me later what comments they had to make and I would get so turned on and we would have great sex. Sometimes, out of the blue, she would ask me how long it had been since I last jacked off. No matter if it was that morning she would ask me if I could do it for her right then. I always did and never disappointed her.
Try it. You'll like. Don't beat him(pun). Join him.