It depends on the situation and how the couple really felt. If they didn't care about their other "significant" then they might not be too hurt. But if they really loved or like the other person then that might be heartbreaking and might as well try not to date for quite a long time.
Well if this is multiple choice then tell me but other than that I can tell you what I personally think. Think of a fire, a fire might get bigger when it is hotter and it can even change colors but most of the time it does not get much brighter once it reaches a steady burn. Stars are kinda similar they can be big but not bright and vice versa. dwarf stars are a tad bit different but then again I will remind you that I am not professionally educated on this topic. the properties that determine such a star can be density, heat(of course), and chemical makeup. Density plays the largest role in such a situation because if the star is not dense but is made of a very hot material then a lot of the time it will be dim where if it is highly dense with a very hot material then often times they are very bright. I don't know if this helped but I hope for your case it did ^-^ I gave it my all XD.
I'm pretty sure the answer is A. The first one.