Loving someone is not the same as being faithful.
I think it is possible to love any number of people simultaneously. This should not be confused with a promise of fidelity.
If you have promised someone that you will be faithful, you don't need to love them to do that, (although it makes it easier). You simply have to keep your promise.
Most of us think that a lack of fidelity equates to a lack of love.
I submit a lack of fidelity equates to a lack of self-awareness in making the promise in the first place.
Don't get me wrong, I love my wife and I know my faithfullness to her empowers her, so I offer it freely without any reservations. This doesn't mean I don't love anyone else. I have chosen my wife above all others, so my actions are guided by that choice.
"In love" and 'love' may not mean the same in this context. Is it possible to want to be with more than one person? Sure.
Is it moral? Depends on who's involved and what has been promised.