He Opened Up A Little About His Mom ...

My foster son opened up to me a little about his mother. We are in the process of adopting him. His 15th birthday is next week and I wanted to know what he wanted to do, but he said he doesn't celebrate his birthday. I asked why and he said "My mom told me it's the day her life ended". I was shocked. I decided to ask. " What was your last birthday with her?" He said his eighth. Then he told me something really disturbing. "I got in trouble that morning for wetting the bed. She beat me with a belt. The rest of the day she was just mean. Her boyfriend got mad me for not doing the dishes. So he beat me and she let him. He did something else... But I can't remember.. I blocked it out". That's it paraphrased. I hugged him tight and told him he's gonna have the best birthday ever. However he pushed a little and said he would really rather not celebrate his birthday. Can I have some opinions. Should I just not give him a birthday or show that his birthday doesn't have to be a bad memory. I know he doesn't want a birthday, but I feel he should know what it feels like to have a real one.