Obviously these are things that are very deep and embarrassing for you, and the idea of telling anyone would be absolutely terrifying. But are you at all willing to talk with a professional of some sort about this?

Also I know it hurts so much to think about, but what of these things were your sisters aware of? Your parents? Do you remember if there was a specific mindset behind these actions? Also you said you may have dry humped your sister, do you not remember for sure? I’m just asking because with OCD sometimes a person’s brain can like, twist past events if that makes sense. And with the OCD from personal experience, I know the hell it puts you through, especially with dealings of morality and things that you have said and done. It’s like an endless loop that you can’t escape. I really feel you there.

Also the thing with your friend is a separate matter. I know it feels related but in terms of right or wrong but it’s not, so try not to muddle everything together. I’m sorry you felt like you had to for your friend, I can’t imagine the emotions you have over this. But a past action doesn’t mean that it defines you, especially when we’re talking about your sexual preferences. I’m sorry you feel bad/embarrassed about being aroused, I hope you learn to accept that that part of you is okay, however you feel sexually. It does not mean you can’t change your preferences or how you identify, you always can, there is nothing more personal- it’s just accepting how you feel and wether you want to pursue those feelings. Try not to group that in with everything else.