If love is a chemical reaction......

If love between two individuals is a chemical reaction, what is the role of the third party?

Is s/he the catalyst?

If so the reaction will be carried out anyway just that with the third party, s/he accelerated the inevitable.

Jesse: (Looks away distantly.) I have these dreams, you know, that I'm....stnading on a platform and uh, you keep going by on a train, and....you go by, and you go by, and you go by, and you go by, and I wake up with the fucking sweats you know? And then I have this other dream, oh.....where you're pregant, in bed beside me, naked and I want so badly to touch you, but you tell me not to and then you look away and...and I ... I touch you anyway, right on your ankle and your skin is so soft and I wake up in sobs, alright? (Inhales deeply.) And my wife is sitting there, looking at me, and I feel like I'm a million miles from her and I know that there's something......wrong! (Celine reaches out to stroke Jesse's face but pulls her hand back before he sees her.) You know, that I....that I can't keep living like this, that there's gotta be something more to love than commitment. But then I think that....I might have given up...on the whole idea of romantic love. That I...I might have to put it to bed that...that day when you weren't there. You know, I think I might have done that.

- Before Sunset