A difficult conversation can be paused with a clear promise about when it will resume.

Stopping a hard conversation without saying when it returns is experienced as being dropped. The other person cannot tell whether they were given a break or quietly abandoned, so they either keep pressing or spend days rehearsing what went wrong. A pause with a time attached is a completely different thing. It says the subject is still ours, just not right now.

If you need to stop, name the hour or the day you will come back to it. Make it soon enough to be believable. Then return at that time even if nothing is solved, because keeping the appointment is what makes the pause safe.