This story happened a couple of years ago. It really happened and still makes me (us) horny when we talk about it.
My girlfriend and I went for a weekend trip to an island to get away from all daily obligations and 'things to do'. This usually means sleeping late and having lots of intense sex with long massage and masturbation sessions (and other activities that do not belong on this website).
Usually we cannot wait to get physical as soon as we arrive at our destination. But this time we decided to take a walk on the beach first. It was a beautiful wide beach and a cold but sunny day and the sun was already getting low. We couldn't help but get romantic and started kissing intensely. I immediately felt my dick swelling and soon it was hard and throbbing in my pants. I started grinding it against my girlfriends belly and she started moaning silently when she felt it pulsing against her belly.
We were not alone on the beach but the people I could see were far enough away not to spot the 'finer details' of our actions. Nevertheless I was shocked when I felt my girlfriends hand unzipping my pants and searching for my cock. When she found it my hardon became almost painful. While our tongues moved around each others frantically, she started pulling on my cock. The head was already oozing precum so her hand started making squashy sounds. I started to thrust my dick in her hand again and again. By now the motions we made were hardly 'finer details' anymore, so people must have noticed.
When I realized this I felt a huge orgasm coming and within seconds I shot four of five thick ropes of sperm against my girl's belly and all over her shoes. I almost collapsed and gasped for air.
After a while I recovered and we tidied up and walked to the hotel and there I repaid my girlfriend in kind for her services.....