<human>: I have met a girl three years ago, let's call here Sarah. Sarah was always a little weird and kinky. We dater for a month then we broke up, because we didn't meet often. Now Sarah is 16 years old and myself is 19 (male). And we have been dating for a month now, everything seemed fine until yesterday. 

I went out with friends and I brought Sarah along. We drank a lot and got wasted. One of my friend(M/18 he is a classmate)  was staying at my house since he was living a few cities away.

We had a blast and a  lot of fun, we were in a pub btw. So we were walking home around 4amish the three of us(Sarah friend me) because Sarah lives the same direction as me.

I had the idea to invite her into my house cause why end the night right that time. So we went inside, turned down the lights and lied on the bed, watching a video on my phone, and Sarah was between me and my friend and I started making out with her, while friend was touching her. I noticed it but I didnt really care. 

So we progressed further and we ended fingering her. After that I came to my senses and told her, that she should go home. After she left we talked a little about my friend and I told him I don't feel bad about it cause if I were him I would have probably dome the same. 

I met Sarah today and we talked about it, and she assured me that it's not gonna happen again. I also started feeling a little worried/bad about it, because I just feel a little bit cheated. So I really don't know what to say to my friend tomorrow and how do you feel about it.

Can you summarize the given text in a few sentences?
<bot>: girlfriend(F/16) and friend(M/18) myself(M/19) got wasted ended up fingering her and not sure how to feel about it.