I'm a little torn here. You genuinely thought the boyfriend was cheating and even had "proof". But you were obviously trying to use it to break them up for your benefit.

You should have said, "That's amazing! I'm poly too!"

So why can't she be polyamorous with you, too? The more the merrier!

I'm sure that being a snitch is a very attractive trait to her. Great strategy, rat fink!

your heart was in the right place but your intentions were not.

Were you thinking if the broke-up then she's guarantee to get with you? This may be a little harsh, but if she is not with you now, chances of her being with you later are not that high. She knows what she wants (and if she is poly, she'd be down to share).

Kinda creepy, my dude.

The fact that you said "my crush" instead of "my friend" literally says everything anyone needs to know about this story. And you ignored her telling you to drop it? You suck. You are NOT friends with this person, you see her solely as a conquest. Leave her alone.