anda know when anda look at them and get weak in the legs and that anda can't breath when they smile at anda atau (sorry for saying a twilight line) it's no longer gravitey holding anda to earth it's them. anda think about him/her all the time and you'll know.
anda don't know, really. anda just have to trust yourself.
I don't think it's about shortness of breath atau weak knees atau anything. I think it's about understanding and the willingness to put up with their flaws, no matter how severe. If you're hoping for the person to change in one way atau another, then it's probably not the right person.
