It’s amazing Belle isn’t more fed up with the fact that every time someone discovers something unsavory about Rumple, their first thought is “Hide from Belle and blackmail Rumple!”
I actually have a far-fetched theory that the shears have to be used willingly – i.e. you can only use them to cut away your Sav-estiny, which is why Jafar gave them to Aladdin, instead of, you know, just waiting for him to fall asleep. So Belle would have to want to cut away her destiny, and I think that if she discovered this “romance,” she would be pretty motivated to do so.
I also have a suspicion that Rumple’s self-loathing is strong enough that he believes Belle and the baby would be better off without him, but that he also knows he would never have the strength to cut their ties himself, thus setting this up.
I very much miss Rumple being the smartest guy in the room. It is possible that there was a deleted scene where they couldn’t get his brain back after Zelena needed it for her spell, and they wound up splitting Charming’s so they could each have half instead?