When is an emotional attachment to someone unhealthy?

So there's a guy I've been talking to over the phone for some time, he is going through a breakup and I've been trying to help with that since I had a rough time with a break up in the past too.

He also may come to my country to study next year and I've been telling him with things regarding that.

However I started to feel like maybe I'm too attached to him now, we have never met irl yet so its like we don't really know each other and I felt down after we didn't talk for a day and now I'm feeling like thats a bad thing; it is

The reason I think is bad is when I get too attached to people I start feeling unhappy when I'm not with them and wanting them to take care of me even though I was doing fine before that; I start to have difficulty in my daily responsibilities sometimes because its on my mind that I am upset or feel down from it.

We have spoken about this and we are going to talk a little less but I'd like peoples input please and anything I can do to cope and focus on something else.

Usually I am quite independent but it all goes out the window sometimes. BTW this isn't romantic attraction, more like a very best friend idk.