You need to stop letting small things like this get you that depressed. I'm not trying to be mean, but it will save you in the long run if you get into an actual relationship and it doesn't work out.
First off, you guys did not love each other. You can't love somebody that you talked to for one day. It bothers me today even when people are in an actual relationship for a month or two and they start saying "i love you." A few months time is not enough to love someone. You may care about them, but you don't love them. For her to say I love you over an instagram photo is boarder line psychotic.
You should text or talk to the person for awhile, then start hanging out for a few weeks to a month, and after that is when you should both decide if you want to be in a relationship. Not after 2 hours of texting.
I know it feels like stuff when something doesn't work out, I've been there. But honestly a one day thing is not something to get worked up about, it shouldn't even be considered a "thing." I understand you are probably to young to see this but one day you will realize how stupid this was if you even remember it at all.
Like I said, her saying I love you randomly over instagram should have been a red flag alone. Don't let it affect you.
