Brother's best friend....?

So I'm in a weird situation.. A friend of mine, who was my friend first, started hanging out with my brother. So after my brothers life threatening car accident last March (2015), he moved in with us so he could help him get around the house & what not.. Long story short, he moved out, I moved out & im living in my own place. But before we both moved out he lived with us for two months. In those two months, he told me how he felt about me. He's so taken with my daughter. He loves her to pieces, her father isn't around. So yesterday he came to my house to help me with my car. He asked me to be his girlfriend & I said yes. I've pretty much liked him from the get go. I just don't want my brother to think I'm taking my boyfriend from him. What should I do? Should I tell my brother or keep it a secret? He's already teased before we started dating saying things like "did your boyfriend go to work?" "Why aren't you with you boyfriend?"