Some specific memories
I have written on here before in the story "Masturbating my sister" about the sexual relationship my one year younger sister and I developed in our teens, based on a kind of role play. It was a bit like doctors and nurses for horny teenagers. We progressed from touching each other's private parts, sometimes to orgasm, to dry humping. Some specific memories of this still turn me on today.
One is the first time I sucked her tits. I remember we were in separate beds in her room, which were at right angles to each other so I had to lean over e headboard and we both had to sit up. I was occasionally allowed to sleep in there when our older sister was out and we had visitors and something sexual happened every single time. I guess we were both aroused at the thought as soon as we knew it was going to be one of those nights. We even started to work out ways of blocking the door so we didn't get caught in the act. Well on this occasion our "characters" had been flirting a little and started to kiss and I was kissing her neck which she loved. Her breathing got ragged and I just pulled up her nighties. She more or less pushed her tit into my mouth. I remember more than anything else that there was a slightly musky smell to her boobs. I didn't so any of the kissing and teasing I would do now, just closed my lips around it and sucked. She seemed to really like it. I actually can't remember if any thing further happened that night but it's a vivid memory sucking her tits.
Memory two is of lying on a bed teasing the insides of her thighs for ages, till they got red hot and she was clearly dying for me to finger her, but her "character" "wasn't that sort of girl". She ended up changing character to someone else, she was obviously that horny and I remember her getting on top and grinding her naked pussy on my cock through my trousers, while I sucked her tits, then me rolling her over and rubbing my cock against her cunt until I came in my pants.
Memory three is one night we went quite a long way, taking it in turns to touch each other between our legs and stopping, often just short of orgasm. I started to finger her from behind, I guess touching her g-spot and when I stopped this time, she said "Maybe I didn't want you to stop." so I started again and I am pretty sure she came. She also wanked me, but not to a climax. We were interrupted shortly after and I remember going to the toilet and as soon as I touched my dick, it exploded everywhere.
Final one for now is a memory of giving her an all over massage, starting on her neck and going all over her body very slowly until my hand found its way into her knickers and very easily found her hard clit. She was soaking down there and it seemed to take only a few gentle rubs on her clit for her to very obviously come to a shaking orgasm, facing away from me. I was actually so excited by it that I came too, my first ever no hands, no stimulation orgasm.
We never discussed this at all and it went on for most of our teens, at least till I was about 18 and it stopped when we started seeing people "in real life". The memories are a mix of guilt and excitement but overall I don't feel bad about it and suspect it is not that uncommon. I hope she feels the same. Nothing has ever happened like that between us as adults and nor would I remotely want it to. I guess the excitement more than anything is based on my first experience of sexual contact with another person. We both needed an outlet at that time in our life and it was "safe" experimentation.