Asymptote

Everyone who have studied math in their life must ever heard 'asymptote'. Well, according to one-web-that-I-found-by-googling :

An asymptote is a line or curve that approaches a given curve arbitrarily closely.

Not only in coordinat system like in math, we also usually find this phenomena in our dramatic-life. This asymptote person could be a guy who adore and love someone, but nothing happened between them. No matter how hard he tried to be as close as possible, they never came together as one. And that's just the way it is. As always.

So in my opinion, asymptote is something that approaches but not falling together.