No this isn't some new expansion pack or DLC, it's my reaction to the game last night. Let me set it up for you. I was kinda curious to see how the game handles multiple romantic relationships, so I created a "man-whore" or more specifically, a "player". A "player" is typically a guy who goes after women (many, many women) just to have sex, nothing more. (I'm not like this in RL BTW, just wanted to see how far it goes in the Sims).
Initially I was more after the relationships - I wanted to see how many girlfriends I could have at once. Well, the game allows that with no issues, but your Sim has to be ultra-careful while wooing potential love interests in public. Other sims may notice and one of your girlfriends could decide to confront you about it. Then you have to woo all over again, though this time around it may take a lot more work. Some good traits you'll want is Charismatic and Good Kisser as they "unlock" other interactions which help in creating a relationship. Schmoozer is another good one.
This soon evolved into how many women (married, single, in a relationship, old, whatever) my Sim could bed. This was working quite good for a while. All you need to do is make an introduction to a prospective subject, then invite them over to your place (at your own convenience) and get to work wooing them. With a receptive subject you may be able to sleep with them that same day, while others may take quite a bit of work - especially those which are married or in a relationship. I never used the "propose going steady" interaction, I wasn't interested in keeping someone long term, ahem.
Anyhow, I was bedding a lot of women (think at least 10) so it was hard to keep track of all of them. But what got me guilty was after sleeping with a gorgeous girl, my sim got up to grab a bite to eat, so I didn't see what she was up to. After I asked her to leave, my sim decided to get some shut-eye, and lo and behold my bed was made (I never make it myself). So this girl was sweet enough to make my bed for me even though I planned to never see her again. I think she even put some books away into the bookcase without being asked. Talk about a guilt-trip. I was both sad and floored at the same time. Needless to say, my wild days may be numbered: I found a keeper!
Now if only I could remember who it was...