<human>: I'll give you some context first; I'll try to do so as compacted as possible.

After I broke up with my previous girlfriend, I stayed friends with her older sister. This grew into a de facto relationship. However, she never wanted to upgrade it to an official "girlfriend-boyfriend" relationship, because she didn't want to hurt her little sister- (and my ex)'s feelings.

This has been going on for a couple of months, and we are in love with eachother. However, her saying she doesn't want to make what we have into an "official" relationship means to me that she doesn't want to make it mutually exclusive.

So it happened that a few days ago I started to flirtateously sending facebook messages to a long term FWB, very very explicit messages at that. Now my "girlfriend" has read these, and she's super angry and claims to not even want to remain friends anymore.

Am I unreasonable for interpreting what she has been saying as a rejection of a mutually exclusive relationship? Am I in the wrong for pursuing other women? I understand her anger, as I would also find it devestating if she fucked any other men. But then why would she say she doesn't want a relationship? 

Any thoughts or advice would be greatly appreciated.

Can you condense the text into three sentences or less?
<bot>: > *long term unofficial relationship with ex's big sister turns sour after she found out I had sexted another girl. Not sure if I'm in wrong.*