Frustrated...my baby is hurting

Our 10yo AS has had a couple of rough days. A friend's child asked him about why he had to be adopted, why his birthparents couldn't take care of him, ect. He did well with the whole exchange - it took place outside, so I didn't hear any of it - but after everyone left he came to talk to me about it and ended up in tears. Then again in tears this morning saying he was still sad about the same stuff from yesterday. Before we adopted him - just 3 months ago - we realized that some openness would be good for him. He has 2 younger siblings, but they don't remember their mom and don't even recognize her as their mom in pictures. Their final visit was almost 2 years ago. We never met bm as we got them from another foster family as a straight adoption. I contacted mom through an e-mail account I set up for just that purpose. We do have contact with a maternal biological relative and I got bm's info from this person. BM was originally very excited that we wanted any type of contact. I sent her photos then and told her I'd send her photos and updates at least 2 times a year. We got some great photos done around the time of adoption, so I sent her a picture of the 3 kiddos. I never heard anything. We had professional pictures done a few weeks ago and I sent her an e-mail telling her if she is willing to send me an address, I'd send her a new photo from the professional. Still I heard nothing. So that brings up to now. My oldest is wanting to know if I've heard from her and if she is okay. I sent an e-mail yesterday basically telling her he is asking about her and I was hoping she still wanted some contact. I've heard nothing. My concern is that bio dad may have gotten to her - this is not a good thing or she's fallen off the wagon, so to speak. If I hear nothing, what do I tell him? I can get info from the other relative, but I don't want him to believe she is in contact with us if she's not. I care about her, because I love her son but I'm frustrated with her. If you've stayed this far, thanks. I just hate to see him hurt so much. And it's a hurt I really can't take away. He does see a therapist.