Search Results: online dating problems

So I met this girl on a website, not even a dating website more of a social media website. We started talking about a month ago and just random chit chat. She really started to open up because she trusted me that I wasn't a creep, so she told me her real age and where she lives. She purposely lied for obvious reasons, which I would too if I was a woman and I don't hold that against her.
So this weekend was great we really connected over it. Starting Friday night until now when she had to go to bed. It just happened I don't know how it just did lol. Turns out she is 17 gonna be 18 very soon. I am 23. I don't mind the age difference at all, but she is still in high school and I just don't know about high school girls as being in a serious relationship. We both want to meet and she only lives 51/2 hours away from me. I do not want to date her now. I want to meet her first and see what happens.
The problem is I am starting to fall for her and I think she is falling for me. She texted me today that every time she gets a message from me she smiles and she said she wanted to cuddle with me. She likes teasing me and I like teasing her. She keeps sending me kissing emojis. I miss her when we are not talking and so does she. This is all too new for me so if anyone with experience with online dating I would be very grateful to them to comment their opinion.
My other problem is, I am a single guy, I have been talking with another girl who is in my city, we haven't met yet but we both want to soon. I met her around the same time as the other one.
Both girls have their head on straight and are really nice, and I am both attracted to their personality than their looks! I have never been in this situation.
Do I need to tell her I am talking to another girl? I feel like I should. I don't want her to wait for me either if she meets another guy. Can you really know a person until you meet them or is texting fine? In short, what the hell do I do?

I'm sure you're all aware that snooping and creeping leads to paranoia and overthinking... well I did it anyway and im kinda paranoid and confused now and i'd appreciate some opinions!

Ok so me and this girl i met off Okcupid had a "thing" going on for awhile. Although we never became official, we deleted our accounts for eachother and we were pretty committed to one another.

I'd say we had a "thing" going on for about 2 months and a half. We had a lot of problems during that time, mainly because she's suffering with alcoholism and depression (but now being treated). Anyway what ended things was: her taking a COMPLIMENT the wrong way (alcoholism f*cking with her mind?) and she totally blew up at me and told me off.

she then was talking about how she made plans to hang with some new guy, then fast forward a week later she said to me they did stuff (she was angry at me, thats why she said that. if its true or not, i dont know. i dont think it is because she's back on Okcupid a week later ya know?)

anyway now onto my main question. So my friend stumbled across her profile online Okcupid again. i told my friend to talk to her and eventually ask her about her experience on the site and the most recent guy she talked to. She talked about "the most recent guy she talked to" was "a dickhead and a liar and we dated for 4 months". And my friend told me the reason she's back on there is because "she dated a guy for a few months then went back on because they stopped dating RECENTLY"

I'm confused because me and her never dated technically, we just "had a thing" for 2 1/2 months, not 4. And I dont recall her ever yelling at me and calling me a liar. Was she dating a new guy behind my back? I'm really confused. Could also be that my friend, who talked to her, doesn't totally remember the exact words she said. cause he kept saying "i think she said __"