What can I do and what would happen to me if I am being accused of rape?

Alright so this is a kind of long story. I have to tell it all for you to understand. My fiancé and her sister were over at the house drinking. We were expecting friends to show up but no one did so we ended up drinking all of the alcohol we had by ourselves (bad idea I know now lesson learned). Long story short we were all blackout drunk, they both ended up throwing up I didn't so I continued to drink. At the end of the night we somehow all ended up in our bed (not sure how I don't remember most of the end of the night. We woke up the next day and everything was fine. Went to eat dinner at her grandmas like we always do with the family and her sister was there and sat by me and even talked to me while we ate in front of the TV. A week later my truck gets keyed and the tires slashed with the words RAPIST on the side. That's what got me thinking, I started thinking really hard what this could be about and I started to remember that night. We were laying their falling asleep and I must have gotten excited or something because her sister started grinding from me and being the drunk assholes we are it went from there. I knew immediately what it was about and told my fiancé we slept together. After her family found out I sent all of them a long heartfelt apology knowing that my marriage was ruined and I have lost everything. Then a couple days later I found out her sister is telling them that I raped her. My fiancé was in the room and knows that that didn't happen, she knows because she was there in the same bed in the same room, how would I even manage to rape someone like that, what did I do rip her pants off and force her to do it without her even making a sound? She even forgives me because she knows how drunk we all were. Somehow being the amazing women that she is wants to come back home and be with me. Here's where the problem starts.