Is it normal for a *brother* (good friend) to do this?

I am an 18 year old male and in my life, I liked (more than a friend) 4 different girls. I liked (still like) this girl I met in 4th grade. And I reacently graduated. I don't see her that much though because she moved in 5th grade to a another city and transferred to a different school. I still see her sometimes. Then I met this girl in 7th grade. She hated me that year but then we became really good friends in 8th grade and 9th grade. (shes still my friend but I havent talked to her in a while) Then I transferred schools the next year and finished high school in this school. I met these 2 girls when I was in 11th grade. And I have this one friend who I treat like a brother. Recently when we graduated, me and my *brother* started to hang out more and party a lot. Anyway when me and him were at this party we went to in the summer, I ended up seeing the girl who I met in 7th grade. Me and her were happy to see each other because we havent talked in a while. So I introduced her to my *brother* like any person would do. So let left them alone to get aquaintanced and I went to go talk to some old high school friends. About 20 minutes later I was going up to them and I saw them flirting and what not. So I got really jealous but I didn't want to start anything anything because I would end up getting kicked out. So I left the party and went home without anyone knowing. So I havent talked to my *brother* for quite a while. So about 2-3 months ago, he wanted to chill at my house because he was really bored. So I said whatever. And I was busy talking to the one of the 2 girls that I liked on oovoo. (BTW, oovoo is a a chat thing similar to skype if any of you didn't know) He ended up at my door so I said to my friend that I will be back and I went to open the door and then he said he will be chilling in my room while I went to get something to eat because I was really hungry. Then I just remembered that I had oovoo open with my friend waiting there. So by the time I went to my room, they already started talking. So she said that she wanted to talk to me privately for a second, so my *brother* left the room while I was talking to her and she said that she likes him. I was upset instantly. so I said I would be back again. So my friend starting talking to him again and they ended up texting each other and what not a few weeks later and then they started to go out. I was going crazy with anger. My *brother* and the other girl who I met in 7th grade were still being good friends at the time. (better friends than me and her were friends) This is all 2 months ago and I'm still upset because he still goes out with her and talks to the other girl and now a week ago, I find out that hes friends with the other oovoo girl that I mentioned. If he ends up being friends with the girl I like from 4th grade, then I don't know what I'll do. Should I talk to someone about this? is it normal for a *brother* to take the girls you like?