How old was your brother when the sexual experimentation started?
How old was he when you two ended your sexual experiments?
I am unwilling to call it abuse, cause up to 10% of kids in some societies experiment with sex ... and it is not uncommon that siblings "use" each other for sexual pleasures and experimentation.
There is a large number of kids who discover self-gratification and practice it at the age of 3 or 4.
It is believed that kids as young as 2 could experience orgasm.
As you said, he liked it too, at least later ...
Our experience may change our ability to fall in love.
If you are born heterosexual, and you as a girl, live in the same room with an attractive, incredible, smart girl, you may develop feelings for her, even if you really are not born homosexual.
There are many people who are heterosexual (attracted to the opposite sex) but with possibility to become bisexual, suppose they meet the right person of the same sex. One single person can change everything.
I don't think your experiments affected your brother's sexuality. The reason I don't think so, is because he seemed to like it too.
If he was disgusted by the sexual experimentation, it could have had negative effect. He could start hating women. But, he seemed to like it, according to your story.
You should definitively talk with him.
Many of your mental problems could be caused by huge guilt you are feeling, guilt that can only be cured by talking with him.
Both of you are now adults, it is time for behaving like an adult.
Some people think it is difficult to talk openly about sexual secrets.
You did it.
Now, the next step is to talk with him.
You can do it.