Accidently cheated on my boyfriend with his friend?

Anonymous
I accidently cheated on my boyfriend with his friend. We were all at my house (my bf, me, his friend) because we were working on a school project together and my boyfriend had to leave early and left the two of us to finish the project. My boyfriends friend started being flirty and touching me and at first I thought he was just playing around but we ended up having sex. I haven't told my boyfriend yet because I don't want to ruin our 2 year relationship and It's already been 2 months this happened and he has no idea. I feel kind of bad though. I know I shouldn't feel bad because his friend came onto me and they aren't even that great of friends. I think they secretly hate each other. We are all 17 by the way. Should I feel guilty? It's been so long so there's no point in telling my bf right? I can see a real future with my bf so I don't think I should tell him about accidently cheating on him. He seems to really love me and I don't want to hurt his feelings.
Updates
+1 y
If you're just going to judge me don't bother answering. I made a mistake ok?
Updates
+1 y
Hah
Accidently cheated on my boyfriend with his friend?
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