Scale from 1-10 how fuck up is this

Wasn't me who did this. Just want to show my sister so she can understand how absolutely terrible what she did was.

How fucked up is it to cheat on your boyfriend with his sexual abuser. Not even use protection, and then give your boyfriend an STD. She can't seem to understand why he's questioning if he wants to be in a relationship with her anymore because she made a mistake... She's saying it's a mistake and the only reason he's rethinking their relationship is because who it was with and that he wouldn't be doing this if she had cheated with someone else... She really doesn't see how much up this is.