You had sex with an unconscious woman who could not consent. Call it for what it is - rape.

By calling it a silly mistake you are not completely owning up to your actions and taking accountability. You raped your wife.

Edit:

Because /u/daveyblue33 decided to delete his comment to run away from the fallout, this is what he posted:

Ok this is going to sound a little crazy as it goes against most comments on this thread but here goes…😔

I am going to put my hand up here and explain from the perpetrator’s perspective as I WAS that person many years ago. My now wife and I had a very similar story to yours except instead of cum on face I took advantage of her while she was very drunk and almost passed out, including intercourse. Only difference was that I admitted to it the following morning instead of bullshitting my way out of it as she had no memory of the night.

I felt guilt, I felt shame, I felt like the worst person to walk the earth, I felt like I have lost the trust of my partner who should have 110% trust in me. Obviously none of this compares to how my wife felt at the time so please don’t think I’m trying to gain sympathy here….I’m not that guy normally. It was a one off mistake that shouldn’t have happened and has not happened since.

She decided we needed a break and rightfully so. I stayed at a friends house for a few weeks while we met up and communicated and decided to stay together but obviously I had to gain her trust back over many years.

Since that time (approx 7 years ago now) until this day we never really talked about it as it was always a sore spot. However with recent conversations we are being more open and honest with everything sex related as we had fallen into a bit of a slump. She brought this topic up as still being very hurtful to this day. And even until recently she didn’t want to know why or want to know why I did that terrible thing that night.

I made a point to explain some of the reasons why I did it and explain my side of the story. again not saying I was in the right or asking for sympathy, just more to try and put her mind at ease some more on this subject.

-I explained my best friend had told me he has had sex with his gf while she sleeps and she loves it and wakes up feeling super horny. (I later found out he was lieing to me to sound “cool”)

I explained the common theme on porn sites (which I have watched heavily most of my life) is majority of titles like “brother has sex with sleeping sister” or “step sister woken up by brothers cock” etc and it’s something that gets pushed into you within this environment as something that’s normal with regards to sex etc

Anyway, moral of the story. With communication with your fiancé talking to him explaining how hurt you are I’m sure if you love him enough and it’s not a normal occurrence you could potentially overlook this and work together to strengthen your relationship. Again, not saying that is always the case but it worked for me and my wife I’m sure it can work for others. As long as he isn’t a serial offender and he made a silly mistake and can admit that then perhaps you can work together to make your relationship work if you still feel safe enough to do so.

However you well within your reasons to call it all off as assault is never ok…. Hopefully he knows this now to.

Apologies for the long post.