I have a black eye after my girlfriend punched me the other night?

i thought it was a slap, but it must have been a punch because my eye is swollen. It happened because i told my girlfriend to go back to her kids and gf and stop treating me like ****. I was sick of being the other woman and the fact that i had started to see another girl motivated me to leave her. The girl that i've been saying saw my face this morning and she's been trying to persuade me to report it all morning. The thing is it will put her entire family life in jeopardy. Her gf will leave with the kids. After everything i still love her but i don't want to be with her. Am i doing the right thing by not reporting it, or is she going to use it to try and get me back. i don't want her but i can't turn my emotions off for her