If regardless of whatever it is we go through, we never give ourselves permission not to love, we are able to maintain balance in relationships. It is of course easier to maintain balance whenever both parties in a relationship have similar perspective.
I dare say, however, that the effect of the middle age crisis on relationships stems majorly, not from the crisis itself, but the perception that passage through the crisis confers the right to be object of love, but not giver of love.
The kicker? If we would focus on loving those in our circle of relationships, this no matter what we go through, the sizes of what we go through tend to become smaller and smaller until we no longer remember just exactly how big it ever was.