Why does this make me so angry?

[Theme57]

ok so I confronted that girl about deleting me on facebook and lying to me about it. I ask he why and she says I just did while laughing because the guy next to her made a joke so she wasnt too serious and just kind of brushing it off like I wasnt worth her effort. This really pisses me off and I end up going outside and tossing my backpack around to release a bit of tension, but am still very irritated for the majority of the class we have together (5 hour class we dont sit near each other). Then during my explanation of a play I read to the class, she was looking down twiddling her hair ignoring me unlike the rest of the group. Now the reason why this irritates me is because I would have been fine if she told me up straight that she blocked me whether or not she had a reason, but because she gave me a nonchalant lie is what got me. Now throughout my childhood (19 years old now) I have had this happen to me many times where people, friends and family would lie the same way and then all of a sudden they were gone and I was alone being ignored.

Now my question is why does this make me so angry? I know I have reason too in a sense, but usually I can brush it off or control it.

I think its because 1) she looks similiar, walks and has a lot of traits like one of my ex's that i had a very very bad breakup with; 2) the trauma from over my life dealing with people doing that to me sets me off, brining old memories and feelings back almost like PTSD; 3) something else im not aware of.
Its not the defriend that matters, I could really care less about that. Its the fact of the lie.
As far as what I did, all I did was say hi to her on FB, she said she was at work and I told her I would talk to her later. Next day I am blocked.