I am not convinced that is is possible to be in love with two people at once. Especially if ''in love'' can be defined as having eyes for no other and being satisfied with what you have. But I do think its possibly to have an attraction to more than one person. Not least because there are different things about different people that might draw you to them.
But what of the person who is seemingly happy and in love with someone, and then meets another and falls head over heels? Assuming it's gone beyond lust, and is not just an excuse for spicing up a bad patch, then what?
I'd suggest that maybe the first person wasn't so great after all. Now in the instance of being in a committed relationship, especially like marriage, I want to make it clear that I don't think it is even slightly okay to move from person A to person B based on who rocks your world the most. But where long term or serious commitment is not necessarily a feature, or where you're in a situation of still finding your way, then I think I have to agree with Johnny: