In my games it tends to depend on the game in question being run. Just for example, right now:
1. In my Roman campaign, Rome being what it is, marriages are not uncommon but usually for convenience's sake. There were one or two significant romances that PCs were involved with (in particular a female player/player character's romantic relationship over the course of many years with Claudius, that ended pretty sadly).
2. In my Three Kingdoms campaign I expect it to be more of the same, but its too soon to know.
3. In my Legion campaign, the Legion being what it is, romance is pretty significant. One of the PCs is playing Ultra Boy, and has been in a romantic relationship with Phantom Girl since pretty much the beginning of the campaign. Some of the others have had romantic entanglements of lesser degrees.
4. In warhammer, there's no romance. There is sex with comely wenches, of course. Also, one of the PCs is a halfling prostitute.
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