Stomach pain / anxiety while chatting with a girl

Hey folks! I (21M) met a girl (19F) online. I've never been in a romantic relationship. I never felt the urge to be in one. I had some school crushes, but I never felt like truly loving them, they were just pretty. Actually, I often get complimented by girls and maybe some of them were even flirting with me, but I just suck at romantic stuff and probably couldn’t even understand any signals. I have some social anxiety, that also doesn’t really help.

Now to this girl. I've never met anyone in my life like this girl. She has absolutely identical humour, we have similar interests and we are both non-believers who live in very strictly religious households, so we kind of share the same misery. She’s the only person I can be my true self with. I always thought that looks would be one of the most important factors for me when choosing a partner, but when I chatted with her, I absolutely didn't care what she looked like. Then we exchanged pictures and she turned out to be super cute.

Now for my problem. We chat a few hours a day. Sometimes as much as six or seven. I'm addicted to chatting with her, even when I'm doing something else, I can't stop thinking about her. Every time she doesn't answer for a few hours, I get stomach pain. I can’t even eat properly. I don't know what's going on, I've never experienced anything like this before. Before going to bed we now always wish goodnight to each other, a few days ago, she didn't answer me (as it turned out she was very tired and fell asleep very early). That night I cried for the first time in about 10 years. It's pure madness. I realise that this is a completely odd reaction, but I don't know what to do. I don't want to tell her all this, because I don’t want her to feel guilty about something she didn’t do.

We’re not even in a real relationship, and I’m very scared to take a further step too early. We always call each other by some cute and funny pet names, so I guess we’re closer than just friends.