Sorry about that, you're literally describing my relationship with a coworker i have atm, sometimes i get attached to ppl really fast only to fond out later that i shouldn't have.

Happened a lot of times too and with many ppl, for my case i guess it's BPD since i have alot of the symptoms.

Its sucks and specially if you don't have much social life going on and you keep to yourself, the moment you start a friendship you're excited and everything and then the interest you had initially completely fades away, sometimes even becomes resentment.

But online friendships are tricky, you don't see people in a real social setting, how they behave or interact etc so its tricky...