Be blinded by rage and probably kill them both.

Not even sure, guess I'd be upset, but realize I was too late and leave it alone.

... I'd be hurt of course, probably would just leave it alone after that and not pursue them

I'd probably run away since I didn't want to see that and then I guess talk to them later about it and see where to go from there

I'm not going to lie, I'd prob break it up and ask if they were a thing, then it'd depend on their response. Either I'd confess my feeling then or I'd get over it after being sad for awhile

Although I'd like to smash their skull in, I'd do my best not to as I don't want to upset my love in anyway. Besides I'm pretty sure this is how it will end anyway... I just want him to be happy...

I'd be extremely jealous and upset and probably blame myself for not doing something about my feelings earlier, but ultimately I'd walk away and try to support them if they really liked this other person. However, let me add that the person better be treating them right or they'll hear from me.

I'd have to deal with it and accept the fact they don't feel the same way. There's really nothing more to say.

Well, it wouldn't be the first time it happened. Move on, I guess.