<human>: Give me the gist of the text in a nutshell

So we've[21m&f] been together for three years and everything's been going great. I came out to her as bisexual a year into our relationship and she took it well. Unfortunately my friend[20m] let it slip a couple of weeks ago that me and him used to hook up before I met her.

She has taken it as a huge betrayal and feels uncomfortable knowing all the time we spend together. I told her it was nothing, that it was a few times when we were drunk. I feel nothing for him romantically and would never cheat on her. 

She's standing her ground and has pretty much given my an ultimatum, her or him. He's been my good friend since primary school and I feel this is totally unfair. I can see a future with this girl, she's smart, funny, sexy and normally very low maintence. 

She's the only person I've ever loved but it still doesn't feel right, deleting someone from my life.

What would you do?
<bot>: My girlfriend found out I slept with my friend before we met and now feels uncomfortable with us hanging out and want's me to cut all contact, what should I do?