My fwb usually calls me by my nickname. Since I've known him he calls me by Cookie.
I had texted him Good Morning and he texted me by my first name. Just curious and maybe no big deal.

That is something you need to ask him. You say he went through your phone, maybe he thinks he is not the only fwb. You two need to stop playing such juvenile games with each other.

Even if he thought he wasn't the only one we're still not a couple for that matter he shouldn't have done that.

He shouldn’t have done what? Call you by your first name? That’s what this thread is about.

Wrong thread oops

You should be asking him why he said/did these things. He is the only one who knows

I am OK if someone calls me by my first name that is no big issue to me as long as he has respect for me.

Nice!