[ARCHIVED] Romantic Relationships decay/become negative fast with no interaction

This is a really odd one. I was grateful at first that my sim couple stayed satisfied in their relationship for so long with no interaction, as they're supposed to be in a long distance relationship. Then one of the sims moved in with the other for a little while. When she moved out again, in one night, their relationship was halved. As others have mentioned, it seems to be that the more the sims like each other, the quicker the decay, which doesn't really make much sense.