What to do? Not sure what is right?

I know that that this is not the place to ask for help but what do I do ?

My girl of 3 years is so cute, super in shape small little thing . Love her to death . But she cheated on me while I was away for work . That is not her , she’s super shy not the cheating kind .
We talked about it , what happened and how things went . She had a quicky with a hot swimmer at the beach . One time thing with a stranger . She said that it’s will never happen again . And I truly believe that .
But it still bugs me and I’m hert .
This is where it gets messed up . I can and will forgive her on 1 condition . I want her forbidden area ! Her little tight butthole . Anal sex . I want to fuck her ass . Then I’ll forget about what she did and take her back .
I told her this , she knows I truly love her and that is what I want to for give her . She crude a little , told me my dick is average sizes and that she so small and that I’ll hert her . But in hert and want her to feel pain .
She agreed to it ! I can fuck her virgin butthole and I will take her back and never say anything about her fling .
She’s coming back home
Am I out of line ?
Should I feel guilty ?
Do I follow up and take her ass ?

If it happens , I’ll share