I think Belle knows that Rumple was certainly no angel before he met her and probably doesn’t concern herself with the details of his actions in the past unless it affects her (For example, Hook went after her to get after Rumple so Belle wanted to know what had happened between Hook and Rumple).
I think Belle knows Rumple will slip up occasionally and he probably always will so whilst she is certainly going to be p****d at Rumple for lying to her and killing Zelena (Belle won’t have the sympathy for Zelena, whenever Belle has asked Rumple not to harm anybody, it been more for Rumple’s sake than the other person’s), I don’t think it would be a deal-breaker for her. Belle knows Rumple has been through a traumatic ordeal, so I could see her sticking by Rumple, as his wife, to help support him through, what was in effect, his phase of vigilante justice.
I actually don’t want Belle to have the dagger because it means that she has the power over Rumple rather than their relationship being an equal footing thing. I like the symbolism of Rumple giving Belle the dagger but I prefer Rumple having his own free-will and him being a “better man” is because he chooses to be, not because Belle has the dagger.
Also I don’t think Rumple likes lying to Belle. Bae has always been the most important person to him so I could definitely see Rumple lying to Belle in order to kill Zelena and avenge Bae. However, now that Rumple has done that, he realises he’s just dug a hole for himself with the one other person he cares about the most. He doesn’t want Belle to find out what he did, but by continuing to cover it up, he’s only digging a deeper hole for himself so he’s caught in another vicious cycle. He’s lying to cover up the lie to cover up the lie and so on. Unfortunately for Rumple, the truth always comes out eventually.
All magic comes with a price!
Keeper of Felix