I cheated for the first time and hate myself

Hello All,
This past weekend, I got blackout drunk and did something I regret. I have never cheated on my SO in the past (been tufter 4 years) and I will NEVER do so again. I don't even remember getting to my house (how I got there, how I got inside, etc.) I feel like my memory was wiped. Next thing I remember was waking up.

My genital area hurt and my tampon was lodged inside of me. I then had a flashback that my friend was over in my bed & I asked him to leave. I do not know how he got there or why. I know he was inside of me at some point because I told him to stop and that I couldn't do this to my partner. I do not know who initiated.

I love my SO more than anything in the entire world and it is eating me up inside. I feel like a piece of trash. I know he is planning to propose soon and I don't feel I deserve it.

Forgive me if this is not the right place to be posting, but I can't help feel that I cheated on the absolute love of my life. I feel sick to my stomach and could really use some advice.

I hate myself so much and I don't know what to do.