Cheated 24M on GF 24F

Cheated on my gf of 4 years with a hooker while i was drunk playing in the casino with my friend.
This was my 2nd time in my whole life in the casino and we were winning and my friend wanted to get a hooker so i took him to one.
He insisted on me also getting one and that he'd pay for it.
I fucked up and hooked up with one.
I am disgusted by my acts the whole person that day drinking gambling and CHEATING is not me.
This is the girl i would have married. I would die for her. I was planning to marry her in a year and a half.
We are very close and our families are very close we have been dating since university and helped me through the highs and lows while i haven't been the best bf. My phone password is her name she has access to my phone whenever she wants.
Not looking for empathy because i cheated i know this is so wrong on so many levels, i can't eat nor sleep.
Even if someone told her i cheated she wouldn't believe him that's how much she trusts me and i broke her trust.
I don't know what to do from now forward with her.
I am getting an std pannel and i haven't seen her since the interaction.
I am in debate whether i should confess or wash it off learn from it and be on my best behavior moving forward?