Fiancee friends with guy she slept with during overnight breakup...

The story,

My fiancee and I had a pretty bad argument one night where I said some very hurtful things and told her to leave in a fit of anger.

She ended up leaving and going to a guy friends house to hang out. It started as game night with a few others. When the other friends left she stayed at the guys house. I know the guy and never felt like there was anything between them, just co workers and friends. After being alone for a while they ended up hooking up and she stayed the night.

I went there the next morning and talked to her and she said she still needed space so I left. She came back home a couple hours later. We talked about it argument and made up, then she told me she slept with this guy. It hurt but I did tell her to leave and that I was done, so I can't accuse her of cheating.

I'm getting over what happened with them but am having a hard time accepting the fact she still wants to continue their friendship even though I told her it would make me uncomfortable. I think I trust her and don't think there will ever be anything happening between them but it still bugs me.

Am I being irrational? Should I trust them and let their friendship continue without doubt? Please be honest and let me hear it.