Withinwalls,

If you can, please do see a social worker / counsellor / psychotherapist / psychologist for a safe space to process how you can cope with your brother moving back with your mum. Your feelings of losing that house as a safe(r) space is important.

A therapist can also explore options with you on how to go about telling your mum if that's your decision.

Some confidential support might be helpful for you, as you're dealing with a lot.

I don't think teenage siblings touching each other sexually is normal... furthermore he continued to do so after you requested him to stop.

Also, you experiencing pleasure is due to natural physiological responses - people can climax from rape and sexual abuse.

Sometimes also one might want the touching on some level even as one hates it. Please do not blame yourself - many people have complex feelings about things like this.

For example, you wouldn't blame someone for wanting attention and affection even if the only attention they ever got was sexual abuse.

For me, I have experienced unwanted touching and on one hand, it felt nice and I liked it, even though I wished it was my boyfriend and not the creep touching me. Fact remains that I desired stimulation and touching, but not with that person.

These feelings of possible guilt because you "wanted it", are all stuff which you can benefit from discussing with a non judgmental therapist.