Honestly, probably not very well. I don't do relationships where there's a first and second place.
This.
I don't believe you can love two people that way.. at once.
I also wouldn't feel comfortable in a relationship where I am in some kind of race, yea I'm winning now but I don't want people gunning for my spot behind me.
If they fell in love with another person/have feelings for another person (and REAL feelings, not just sexual attraction) then IMO their heart wasn't in the relationship they are in :/
Either way, I wouldn't want to be with someone who, while dating me, still had room in his heart to be falling for other people.
IMO when you find the right person. that's it. No ifs, ands, buts or silver or bronze medals.
I would probably end the relationship to be honest, if we are talking about LOVE here.
There are too many mediocre things in life to deal with and love shouldn't be one of them. Anything less than mad, passionate, extraordinary love is a waste of your time.
I am just not interested in the kind of love that isn't all in.. I don't want love that can be measured.
I would talk to them, find out what is what, what they are TRULY feeling (is it love or is it anxiety.. sexual tension.. the enjoyment of someone new) and if it is love..then I'm done.