Hi, Joe! Welcome!
I don't have much to add to Kaliope's words.
Only a thing, you say that you can know someone very well but you suddenly begin to avoid him/her. You don't know why.
Might it be because you are afraid of damaging or ruining a relation that is working well? Could it be because you are afraid of people knowing you better?
Perhaps, there isn't only a reason. I'm only giving some posibilities.

Being avoidant or not, there's something happening you are not comfortable with so have you consider the posibility to talk to someone about it, appart from us?

A hug!