Hello imsorryyy: Thank you for bringing your concern here to PC. I see this is your first post. Welcome to Psych Central.
I'm so sorry all of this happened to you (& your brother.)

Yes what you did with your little brother was unfortunate... for the both of you. But you were a child yourself. And, as you mentioned, you had been "kind-of raped" yourself when you were younger by an older friend. To me this type of situation is one of the great sadnesses of human existence. Too often victims of abuse (sexual or otherwise) then unintentionally become perpetrators themselves. And the damage just continues on.
I'm not a mental health professional. So I can't offer you anything in the way of an authoritative reply to your thread. However my personal opinion would be there really may not be anything you can do to be of help to your brother. (I assume you would not want to, or feel you couldn't, talk all of this through with your parents.) How your brother is reacting to topics such as love or marriage may or may not have anything to do with what you did. (Perhaps it's simply young teenage boy stuff.) But, either way, I think that is something he may have to sort out for himself perhaps with the help of a counselor or mental health therapist. That is something he'll have to make the decision to do on his own though if-&-when the time comes.
The other aspect of this situation that is of concern, however, is what the guilt & shame you are carrying around regarding this incident is doing to you. Guilt & shame can do a lot of damage to a person over time if left untreated. So it may be that, at some point, you yourself may want to find someone you can confide in... again perhaps a counselor or mental health therapist. I think that is about what I can say regarding your concern. Perhaps other PC members will have other insights & suggestions they can offer. My best wishes to you. I hope you find PC to be of benefit.