You can generally tell by the register of the language.
The basic problem is that there are only 3 or 4 situations, they keep recurring, and every teenager who winds up in one of these 3 or 4 situations is convinced he or she is the only one who’s ever experienced it.
The answers are—
1. Get over it. S/he has said that s/he is not interested.
1a. You’ve given him/her multiple hints and opportunities, none of which s/he has taken. S/he likes you as a friend; move on.
1b. You broke up for a reason. Move on.
2. We have no idea. We don’t know if s/he likes you, and the worst that can happen if you ask is that s/he says no.
3. No. Fooling around with your best friend’s bf or gf is de rigeur as an opera plot, and it never ends well. At best, the soprano gets a memorable death scene.
Now, what we need is a script that recognizes teen k3wlt0k and SMS-speak, and presents these set of answers. Lovelorn querents may then search for an answer to their question there, and find it—but they’ll no doubt remain convinced that their situation is like totally completely more unique than anyone else’s, and ask the question anyway.