I don’t understand some people. You see two people (who are close to you) talking… and the automatic thought is that they are cheating on you. Snap response to paint everything black.
But… What IF… Trampled by reindeer… destroyed the surprise gift/party they were planning in your honor.
And if it is a case of infidelity – let them go! It is for your best! They have to remember how they gained such a relationship. They will never trust each other. But you are Free to find better people!