My best friend and I had a very similar experience in the 10th grade in our pool one night while my parents wee out of town. It started out skinny dipping also. We both got very hard an started grabbing each other in the pool and while standing face to face stroking each other he said we should try sucking each other. No argument from me we quickly got out of the pool and he went first and in no time I just had to suck his dick so we got in to a 69 on our towels in the grass. It was very dark ad since we lived out in the country no one lived close to us.
We were really going at it when I felt his finger slowly pushing in to my asshole and it felt so good I let him continue and not long after he stared to finger my asshole he said he wanted to fuck me and asked me If I would let him try it. I said I guess so and after spitting on my asshole several times he was on top of me with his dick stuck up my ass and when he started to fuck me I pushed my ass up a bit so he cold get even deeper in my ass and once I began to moan and move my ass around trying make it feel even better he really gave it to me hard for a short time then shoved it up my ass really hard and started to cum and it felt o good I was quickly asking him to fuck me some more and told him to cum in my ass gain if he could.
We both got excited and he fucked me up he ass a second time and came in me again. he rest of the night and the next day we fucked like crazy an he came in my ass many times and I could not et enough and we fucked all the time and both liked to suck each other off and swallow each others cum. Months latter we had our best friend join in after we made him promise not to tell any one about it.
For a couple of years we had a lot of great sex and the 3 of us managed to keep it very private and my favorite was taking both of them at the same time at both ends and nothing ever felt as good as when they came at the same time. A hard dick in my mouth swallowing his cum while the other one was deep in my ass shooting a big hot load up my ass.
I was the submissive one when we had sex and I really got off letting them use my mouth and ass and getting them off and letting them cum in me all the time was something I really enjoyed. We did a lot of things and got pretty damn dirty at times and they even DPed my asshole many times and would both cum in my ass every time. On weekends they came in my ass many times and it always felt good.