<human>: So, this is my story. I apologize in advance for any ambiguity.

Recently broke up with first major girlfriend (We will call it a 3 year relationship). We met through a shared group of friends and naturally maintained that same group of friends throughout our relationship. During our relationship I had some minor transgressions with one of her friends. Nothing unforgivable but definately some questionable moments while drunk and my (at the time) girlfriend expressed a strong dislike of both my actions and the friend in question. Now, it can also be noted that I have expressed a strong fear (I guess you could call it) regarding my ex sleeping with any of my current friends. And yet, somehow, I've become the one to do this to her.  Over the passed few months I've been trying to create a friendly relationship with my ex. I will always love her and I honestly had (deep-down) hoped that someday we could try to be together again and now that I've slept with her friend, I feel there is no chance to ever try again. I would feel horrible if I dated her again and never told her about this instance with her friend. 

I also want to note that the friend and I agreed not to tell anyone about this happening, but I'm slightly worried that this will come out at some point in the future and it will destroy any possibility of even a friendship with my ex and possibly the shared friends. We were drunk and it was undoubtedly a selfish mistake.

So, I guess my questions for you guys are:

Is it okay if I remain friends with the ex without her knowing?
Am I a horrible person?
Should I avoid 1 on 1 interactions between myself and the friend?
If I do end up dating the ex at some point in the future (say, a year from now), is this something that I should keep to myself or something I should bring out into the open and hopefully move passed?

Or if you have any advice or personal experiences regarding similar experiences Im sure I would enjoy hearing about those as well.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: Got drunk. Slept with ex's friend (also my friend). Want to be friends with ex still. Regret.