Are you all open and stuff? I am just wondering whether in the case of a wedding for example, would you feel awkward taking one partner to one wedding and another to a different wedding?
In which case I would a) see who is available, b) see who is interested and then if you still have a choice alternate and say I will take X to this one but how about Y to the next event? That is fair.
Let's be honest we are not all into the same thing, one partner might love a party with all your friends from the some sporty game thing, whilst the other would rather have their nails pulled out with tweezers. Not everyone likes weddings and other formal occasions either.