I'm not sure this is in the exact vein Ark is looking for, but...
I had a character dating another one for years. He decided to ask her ICly to marry him, after the other player asked me if that was cool with me. Sure! We got the staff approval, etc, and we actually used the big, flashy proposal to start a little plot arc.
Marriage was going well, things were going on, and then the other player approaches me OOC about them starting a family. My character was the sort of girl who would want that, so I said sure, we could bring it up IC. Yay, marital bliss. We updated Staff and got the okay, and so on. (It was a comic game, so for an FC you need okay to do things like marry and so on)
Then I got sick, and couldn't play every night, and big action scenes were hard for me to focus. (yay trying to find the right med for my ills) . So my girl is pretty pregnant, and her husband wants her to go on a space faring adventure, without knowing how long it would take, how her body might react in space, etc. So she erred on the side of caution and said no, she'd be afraid all the time.
A couple weeks later, the other player comes to me OOCly and says my girl is boring now, and he wants out. He wants to retcon YEARS of IC play and development, because she's not doing action stuff anymore. (She's supposed to be 8 months along, at this point) But in reality, I wasn't TSing him, and someone else was willing to, though I didn't know that at the time (Some mavs made it clear later).
He OOCly threatened me, said he would ruin the game for me, he'd go to staff, and so on. I told Staff the threats, etc. They said he could have the divorce, but he can't just wipe years of my character's RP. So he went to the news board, and posted how his character came out of the hospital, that it wasn't his kid, etc etc. (Which was not supposed to be done, according to Staff decision). Staff didn't so much as slap his hand. They took down the post and said and did nothing. He went on a spree with all his alts (even ones that had no connection to my character), to do his best to ruin any RP avenues I still had left, and Staff did nothing.
So yeah. I'm pretty wary of the IC romances at this point. Communication is huge, but understand if you change your mind, it doesn't mean you should/can ruin someone else's whole thing.