My (30M) friend (31M) slept with my (30F) fiancée to “prove she isn’t loyal”

A little background: my friend, let’s call him Dave, went to school with my fiancé, I’ll call her Lindsey. I met Lindsey at a dating event, and we were going to get married in November.

As I said, Dave went to school with Lindsey and had a couple mutual friends, and he told me that Lindsey was big into the party scene. I didn’t really have a problem with this.

About a month ago he messaged her on Instagram and for about 2 weeks he flirted with her and she brushed it off.

Then he asked to meet with her and she declined because she told him she was engaged to me, but kept talking to him and eventually she agreed to have drinks and hook up with him afterwards.

He told me he hooked up with her only to “show me she belongs to the streets” and he’s acting like he did it for me.

I have no idea what to do now. I was made aware of all of this last night. He was my best friend and I just don’t know what to do or think.

Netizen’s comments

And what proof does he have of this? If it really did happen, then he exposed himself too, and they’re both for the streets. Even if he’s lying, you should ditch him.

But seriously, I hope he has more proof than just “trust me bro”.