I had sex with my boyfriend's brother. Would it be best to tell him or hope he never finds out?

Anonymous
I moved to Portland and became friends best friends with a guy who is now my boyfriend we'll call him Ted. We have been friends for a year and have been together since February so not too long. Anyways I also became good friends with his older brother his name will be franky we hung out a lot and he wanted a little more then friendship but I always refused because I didn't see that in him. But one night we hung out and I was having a rough time a guy had broke things off with me and I was pretty upset. So we had more than a few drinks and ended up having sex. The next day I was super confused not sure what to do because I didn't have feelings for him it was to me a one night stand. But when we would hangout and drink we would kiss we never had sex again. Well one of the nights my best friend who is also my co worker and also is also frankys brother ted came over and we were all drinking and ted decided this was night he was going to confront me about his feelings that he has had for me and I had always had a little something for him too. So then it happened with me and Ted. We started seeing each other I told him there was never gonna be anymore because I wasn't sure I wanted a relationship I just wasn't ready and not only that but I began thinking that maybe I didn't have feelings for him in the first place now that I had him but we kept seeing each other because I didn't want to hurt him too soon. But as we continued seeing each other I did develop strong feelings for him and now me and ted are together but he doesn't know that me and his brother hooked up a few days before me and him started seeing each other. I feel bad but at the same time I never ever thought me and ted would get together. Not only that but we weren't together at the time and I don't necessarily regret the night with his brother but I wish it wouldn't have happened because it was a mistake and there was no point in it I had no attraction to his brother nor did I have feelings for him. He is an attractive guy and has so much going for him I'm just not interested. I don't know if I ever want my boyfriend to find out he's always been jealous of his older brother. his older brother always gets the girl, he's got the great career, nice fancy vehicle and everything he's ever wanted. And my boyfriend was so happy when we started dating saying that franky wanted to be with me and came to ted about having a relationship with me asking ted to back down but ted said no. Ted said he usually always backs down because his brother ends up getting the girl in the end but this time that wasn't the case were very happy together. I am afraid that if he ever found out he would never forget it. it would hurt him so much and he is such a sweet guy I don't want him to ever hurt the way I know he would if he ever found out this information. What should I do
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The reason I say I don't regret the choice I made is because I learned from it. It was a mistake if I regret my mistakes then I might as well regret who I am and I am very proud of who I am because even though I have made many mistakes I've learned a lot in my life and if any of you actually knew me in person you wouldn't expect that sort of behavior out of me I'm much more balanced then the average person and I must say have a lot more common sense as well but I am only human.
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And I agree with the person who said to put myself in their shoes and I have decided I'm not going to tell him. I wish it were that easy but it's not. If I were him I'd rather just not know and go on being happy in the relationship. If me and his brother actually would have had anything more than just the one night then I'd tell him. But it meant nothing and therefore is nothing and will continue to be nothing and there's no point in hurting the one I have come to love over nothing.
I had sex with my boyfriend's brother. Would it be best to tell him or hope he never finds out?
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