My step brother out of the blew became randomly over protective? Is this normal?

Anonymous
I moved in with my mom and her new husband, this included her 20 year old son and 15 year old daughter. The other night I found out that my coworker I have been making out with and semi falling in love with got in a relationship with a girl who I frequently saw. It really hurt me because I don't give my time or effort to just anyone. I got really wasted while our parents were out of town and he was in charge. I got dropped off my a friend, who was sober, and started crying the second I got into the house. He hugged me and wrapped his arm around me all night till I felt better. He knew I was a virgin because we went to the same hs and that was my reputation. He came into my work and told the guy what an a**hole he was and what he was missing. He was super reassuring and made me feel better of the whole thing. We fought endlessly when we first moved in. Why is he doing this out of the blue?
My step brother out of the blew became randomly over protective? Is this normal?
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