This happened a few years ago. My wife, who was then my fiancee, and I went to different grad schools, so for a time we were in a long-distance relationship. We would see each other as often as we could, every weekend at best, but sometimes it would be over a month between visits.
Our next visit came when we were both back in our hometown for the Christmas break. Having gone so long without seeing each other, we were both desperate for a chance to have sex. The problem is we were each staying at our respective parents, and that could make things difficult. We were out driving and were about to head to my place because my parents had gone out. We were supposed to meet her parents for dinner, but we had time for a quickie and we weren't giving it up. Or so we thought.
My fiancee then gets a call asking if we could pick up some things at the grocery store for dinner, and to hurry because her sister was also home from out of town and we were all going to a movie afterwards. We were very disappointed as now there was no time to get everything in.
As I pulled into the parking lot, I couldn't hold out any longer. I parked as far back as I could and then began to french kiss my fiancee. As I was kissing her, I unzipped her jacket and began to caress her breasts. She was enjoying it but said "You shouldn't do that." I responded with a playful, "why not?"
"Because, you're going to make me all wet"
I told her that's what I wanted and just because we weren't going to get to fuck, I still wanted her to cum. My hand slowly went to her jeans. I unbuttoned them and put my hands down her panties. She had lied, my kissing and fondling her wasn't going to make her wet, her pussy was already dripping. I started to slide my finger along her wet lips and then began to rub her clit. As soon as I got to her clit she just closed her eyes and began to moan with pleasure, telling me how much she missed being touched. Suddenly, a car pulls in next to us. I quickly wait until they have gotten out before I continue. As soon as they were out of sight, I went right back to it. This time there were no more interruptions and I was able to give her a much needed orgasm.
Now it was my turn. She reached over and began squeezing my cock through my jeans. I was already really hard from fingering her. She unzipped my fly and unleashed my erection. "oh, I've missed your cock so much" she said as she stretched over the middle-console and began to suck on me. I was in such a state of bliss when I could see in the mirror a couple heading towards us, going to the van parked next to us. They'd be able to see everything. My fiancee quickly got up and I covered my cock until they were gone. Once they were I was desperate to continue, but she was very nervous about finishing the blowjob in case we got caught. Instead, she reached over and began to stroke it with her hand. My cock was nicely lubed from her saliva and soon her skilful hand had me cumming into a wad of kleenex.
We both felt so much better after that. It wasn't the fuck session we wanted, but we still both had an orgasm and the riskiness of being in a public place made it such a turn on.