We told my 12 yr old SS this past week that I'm pregnant. I was expecting drama like what he expressed 2 years ago at the possibility of a younger sibling. Instead, he was pretty calm and mildly interested in knowing more. He even wanted to look at the sonogram. I thought things were going okay.

Then this weekend he starts crying. We were at DH's parents house and SS had said he thought his grandma was going to freak out (we agreed, she's been asking - begging - for another grandkid for years.) DH and I thought the crying might have something to do with worrying that grandma would care more about the new baby. Nope. SS is worried that his mom will be 'sad' that DH and I are having a baby. Oh boy. Found out his mom has been playing up the 'victim' card and saying she still loves DH (by the way, she was remarried less than two years after their divorce) and never wanted a divorce and she could never imagine DH and I having any children.
DH was all pissed off and had to leave the room for a bit. See, BM cheated on DH. After SS was born, BM didn't have a job but left SS with DH's mom to go on trips with friends. Co-ed weekend trips. After it got back to DH that BM had been making out and some other stuff with a guy during these trips, DH confronted her about and she admitted some stuff had happened, but it didn't count as cheating for some reason or another. DH stayed with her, but didn't trust her anymore. Fast forward a year or two later and when DH had to leave on a business trip for a week, he found that every time he called home, a male 'friend' of BM's was answering the phone. When he came back, he found men's underwear. DH confronted BM about, but she said nothing happened, but she did have some 'feelings' for this other guy. She proposed an open marriage.
None of this is something SS knew. Instead, BM had told SS that I was the only reason DH and BM had gotten a divorce and that she would never lie and had never done any cheating. I think SS knew this wasn't true since one time he repeated what BM said to DH and DH flipped out and told SS that it had been his mom that was 'doing things outside the marriage.' At that time I had told DH not to tell SS about what BM had done because I don't think the kids should have to hear about their parent's crazy issues. So DH left it at that. (In reality, DH and I didn't have any involvement with one another except as friends until after they had already gone through all the stuff already mentioned. I guess since we started dating when they were separated and not living together instead of being officially divorced - which they we're 6 months after we started dating - in her mind I'm the cause of the divorce.)
But all of this came up again now that I'm pregnant. SS was worried his mom would be sad, and he wanted to know why the divorce happened at all. I guess he might have been trying to figure out if his mom had a right to be sad. He even said he thought it might be 'creepy' that she would be sad. SS said he didn't like that DH and I weren't telling him "DH's side of the story." He said he thought that we thought he was stupid by saying he was too young to hear about what went on. So we told him what BM had done. We cleaned it up some and we repeated to him that he shouldn't judge his mom, and that she loves SS and that we're all human and make mistakes.
In any case he stopped crying. I don't know if we did the right thing or not. The whole thing pissed me off though. I even wondered some if he was sad about the baby, but didn't feel like he could express it. He kept repeating that that wasn't it, but who knows? I hate that something awesome, the coming of this new little person, means having to drag up drama from years and years ago. I wonder if BM wasn't a drama mama if SS would have been able to let the idea of being a big brother grow on him without having to worry about what his mom will think of it. I wonder if he won't want to have anything to do with the new baby after he has to deal with his mom's sadness about my baby.

I just wish I could be pregnant without having to worry about hurting the feelings of someone who hurt DH!

Oh, I got an additional bonus from that weekend when MIL, who pretty much treats me like I don't exist, told me I could call her and just talk whenever I wanted now that I'm pregnant. She also said she would love to stay with us the few weeks after the baby is born. Ha, no. I've spent enough years being shoved to the side when it comes to dealing with SS on the grounds that I'm just the SM to let her shove me to the side on the grounds that I'm just the mom.