Hmong Brother

So, I don't know if my brother is intentionally doing this or if he doesnt know. But I am 20 years old and my younger brother is 18. He plays soccer and wears soccer shorts all the time around the house. As much as I dont want to check out my brother, sometimes you can't help but see his legs and bulge bouncing when he walks around the house. You can totally tell he doesnt wear boxers because I can see the outline of his Hmong cock.

Anyway, since he has been out of school in May, he hasnt found a job or anything, so he stays home all day long and just wears his shorts around the house with no shirt on. When he sits on the sofa or on the ground, he sits with his legs open and sometimes if you look you can see his balls hanging under his shorts. As much as this is disturbing, its also becoming a turn on. When I see this, I try to pretend like I'm watching TV but I glance over every once in a while.

Two days ago, something happened and I dont know if he caught on and it is also turning him on. He was in the livingroom with a white soccer short on. I was sitting directly across from him but we were both facing the tv. After awhile, he reached down to scratch his balls and you can totally tell he got hard because the head started poking out the side of the short. At this time, I was getting a bit horny, so I just pretended like I didnt see it but kept going in to take small looks. At one point, he noticed that I was watching and he reached down and pretended he was scratching so I looked away. When he stopped, I glanced back and noticed that he took out about half of his cock out the side of his short. At this point, I got scared and walked to my room.

Is this normal? What does this mean? What should I do?