I dont think they permanently forget about us. That is why we need to enforce no contact.
They might be temporarily taken up with a new fling, hobby or obsession, but they always come back, hanging around like a bad smell and looking for ways to get our attention or unsettle us. I swear they think they own us- even post-divorce!
They invariably come backwards and forwards, like yo-yos, causing chaos with their instability, changeability, restlessness and wreckless behaviour. The only thing we can do is batten down the hatches, make sure they can’t re-enter our lives.