Confessions: I'm in Love with my Brother

Dear Justice,

I recently met the man of my dreams and ever since we have been inseparable. We share the same values, ideas and outlook on life. We have been thinking about moving together to save money so that we can eventually plan for our wedding.
I spoke to my mom the other day and told her about my new found love and how I want her to met him. She was absolutely thrilled. She wants grandchildren and she wants to see me get married. While talking she told me that she ran into my father's brother at the store and gave him her phone number to give to my dad.
I have never met my dad and wasn't really sure I wanted to. After talking to him a few times over the phone I agreed to meet him. I went to his house where he had several other family members waiting, including my half brother and sister.
To make a long story short when I got there everything was fine until I walked into the den and saw my new boyfriend. My palms immediately became sweaty and I was so afraid because I had never mentioned to him that I hadn't met my father. Here I was caught in the middle of a lie and now it was going to be exposed in front of a room full of strangers.
My dad began to introduce me to everyone and when he got to my boyfriend, he introduced him as my brother. I was sickened and heart broken.
Since then I have been trying to figure out what to do. I am really in love with him and I know that what we are doing is wrong but I didn't do this on purpose and now I don't know how to get out of it. My mother has been pressuring me to meet him and I don't want to tell her it's my brother or that we have continued to see each other even though we know the truth. I am so confused and afraid of losing the best thing I ever had. What should I do?

Hurt and Confused in New York