I once slept with a freshly-minted former student on graduation night. I was in my mid 20s.
I know you want details as to how it started.
Karen(not her real name) was in my class first semester. I could tell she had a crush on me. Bear in mind Karen was not that attractive, but was cute and she was a very sweet girl. Anyway, semester comes and goes. During the second semester Karen's friend, Renee(not her real name) is in my class. At least 3 or 4 times a week she mentions Karen's feelings for me and what not. I don't completely shut it down but I make the point that I'm not putting my job on the line.
Fast forward to graduation night. After the ceremony some teacher friends and I go out for drinks. I get back to my apartment about 11:30 pm. I get on my Gateway desktop and check my email, hop on AIM, and check my MySpace. Renee had sent me a message. In this message is Karen's cell phone number and I will never forget how she ended it, "Don't punk out." I must also add that by this point in time I've been dating a very nice, beautiful woman for a few weeks. Anyways I text Karen. I find out Karen and Renee are at a bar less than 1000 feet from my apartment(which is crappy and cheap and near a college, hence allowing 18 year olds in or not checking fake IDs too closely, not sure which it was) I quickly get dressed again, put my contacts back in etc. When I get to the bar I buy them each a Sex on the Beach(I figure that's what an 18 year old would drink). We make nervous small talk for a while in our booth. I then drunkenly lean in and make out with Karen. At this point we decide to head back to my apartment. Again we sit in my living room making small talk, a little making out etc., I then suggest we go to my bedroom. Meanwhile Renee is sitting out in my living room, and come to find out she went through my phone, got numbers for colleagues of mine she wants to bang, etc. Karen and I do the deed and all the normal rushed foreplay that leads into it. I will never forget what she said after I finished. "Did you nut?" It was so dirty, so crass and yet so sexy at the same time. Anyways her and I lay in bed, talking, cuddling, kissing etc for a while longer. We make plans to meet up again. As the time gets closer I start to feel bad. I know I have no intention of dating Karen, which she clearly thinks is going to happen. So I call her and tell her that I think she's great and very sweet and that I don't think it's a good idea we meet again as I have no intentions of dating her and don't want to string her along. She agrees and we never see each other again.
I ended up marrying the woman I dating that referenced earlier. Still married and have a beautiful daughter with her.