@GMWolf - I'm aware of that, though the two are not unrelated. What I meant is that make-believe relationships of a sexual nature are inappropriate for video games, regardless of whether or not the game includes any explicit (or even implicit) sexually-vulgar content.
I say they're inappropriate because, for one thing, pop culture has the power to shape societies for the better or for the worse. If you depict dating (even without any reference to sexual intercourse) as something mundane or trivial, and you present it to the audience in terms of "dating is a part of life, you should be doing it" or "if you want to be happy, you should get a boyfriend/girlfriend", then your depiction subliminally enters into the audience's experiential memory, which then carries over into his real-world relationships and real-world decision-making. On a larger scale this leads to cultural desensitization which is evident in the fact that many young people today are dating at a very young age (e.g. middle school, sometimes earlier), as if they feel some need to have a boyfriend/girlfriend, though they fail to see the greater purpose of dating beyond just "feeling good".
The essence of "dating" (or "courtship", to use the more proper word) is that it's the first stage in preparation for marriage. Dating is not trivial, and it shouldn't be presented as something trivial. You shouldn't be dating unless you have some intention of getting married, or are at least open to marriage. To date for the sake of dating, or for pleasure alone, without seeking marriage, or for any other motive, is morally wrong. Yet for the past few generations the movies and TV have been bombarding society with the exact opposite message, such that dating at an early age has now become commonplace, and many people don't even realize the true purpose of dating anymore, or see that it's wrong to date for the wrong reasons. (And worse still is that people who don't take dating seriously are just one step away from not taking sex seriously either. So we end up with all these pregnant teenagers, and abortion, and STDs, all sorts of other related problems.)
Come to think of it, even the friendships in Animal Crossing may be going a little too far. Not because they're too sexual, but because they promote a very utilitarian view of "friendship". The player must use the in-game characters as a means to attain better items or a better score. It basically degrades "friendship" down to the level of mere usefulness, which, again, can impact our real-world outlook as well. So this game mechanic is questionable to say the least. But for the dating mechanic, I'd say it is unquestionably a bad idea. Games should promote temperance and chastity, not promiscuousness. But temperance and chastity are more abstract, so I'm not sure how they could be implemented into a simulation game and have the game still be enjoyable. (You could probably more easily implement them into an adventure game or a roleplaying game, but not so much a simulation game.)