Do you remember your first swinging experience? I do, and this is what started me on a lifelong journey of extra sexual fun. It was about 1971/2 and I was 18 at the time. A good friend of mine, Paul, rented a flat in a large old Victorian house close to where I lived. His flat was on the top floor. One summer evening I called round to see him as arranged. I knew he was at home. Paul worked for a TV rental company, remember everyone rented their TV's then? His company van was parked outside so I knew he was at home. There were about a dozen or so bells at the side of the front door, so I pressed his expecting to be let in. No answer, but I could see the front window open so called his name. Those bells were never the most reliable of things! The guy in another flat popped his head through the window, I knew him by sight from my frequent visits. Asking me if I was after my mate Paul he said he was certain Paul was at home. He was about to go out and would let me into the house when he came down. A couple of minutes later I was climbing the stairs up to Paul's flat. The door was unlocked and I opened it and walked in. There was Paul completely naked on top of a girl called Liz who was part of our friendship group. Her legs were up in the air wrapped around him as he pumped in and out of Liz. I don't know who was the more startled, me barging in on them or Paul and Liz being interrupted mid shag! For a few seconds I stood perfectly still, I couldn't take my eyes off Liz'z naked body. Then, and I don't know to this day what made me say this, but I said 'Do I leave, stay and watch or strip off and join in!' 'Up to you' Liz replied, so I started tearing my clothes off and leapt on the bed to join them both. Liz greeted me with a deep loving kiss and said 'Welcome.' We had the most amazing session, then after an hour or so went to the local pub for a drink before returning to spend the night all together. Over the summer we had a few more 3-sums together before Liz and I returned to our respective universities at the end of September. We had another couple of 3-sums we met up over Christmas but they were the last times. MMF 3-sums have been my favourite ever since!