I Was Cheated On By My First Love

She just blatantly disregarded the fact that we were supposedly a so called couple and just got with some other guy. Didn't say she wanted to break up. Nothing. Then starts posting stuff on social media of her and the guy and of course I seen it. SOOOO..... what makes bad worse is she actually originally tried to lied directly to my face and say that was her brother.

I...
Don't...
Even...