Well I live alone, have a regular "date" plus a really good friend who adores me. An enviable situation on the face of it but not all plain sailing. Only by being scrupulously faithful and honest to one can I justify having the pleasant company of the other at times.
The side effect is that it makes the first more attentive - which is a mixed blessing and not what was intended.

I could not have done this as a teenager - only with the maturity of middle age is it do-able.

But as mother used to say "keep 'em mean to keep 'em keen"
and she was right.