Excuse me if this sounds rude- because I'm not trying to be. Nothing is wrong with the way people want to live their lives- if they both agree to it. But here is my personal opinion.

I think true, undying love, means loving only that one person. . . I think it's impossible to truly be in love with two people at a time. You can appreciate and like characteristics of each- but I think REAL TRUE BLUE love, is one person.

That's just me though.