I would be really happy because someone I loved (my wife) liked my best friend.
Also, I'd be relieved because this would free me up to marry someone else next year, if I could meet someone else and fall in love.
I would expect that if twenty years went by, my relationship with both my wife and my best friend might still be the same, unless one of us was too embarrassed to continue contacts.
But people who are younger, as I have been, would be shocked and have to go on a long trip somewhere to get over it.
So, I'd hope to handle it pleasantly and friendly, but if I were to become hyper and shocked, I know from experience that the best remedy is a trip somewhere. Time heals all wounds, but travel helps this kind of wound to heal faster. It's like rubbing ointment on a cut.