Regarding DH do you trust his judgment normally, is he given to poor decision making? No. He met you, got to know you, fell in love.
Does DD care about anything but the sight smell or touch of you? At 2 in an uncomplicated way she loves you.
When she is in her teens and asks about her grandparents or their divorce, will she able to see past any childish involvement and realise a 12 year old can't influence something as critical as a total marriage breakdown? Very probably.
Being a parent ourselves can trigger old memories. You were a powerless child then. Now years' later perhaps you fear your own happiness won't last.
Hindsight is a wonderful thing, we're all wiser after the event. A knee jerk reaction, an adult shifting blame, sadly not uncommon. Neither parent is around to ask. (They might have fobbed you off anyway). Talk it over with someone professional, ask your GP.
Don't under-estimate what you have now. Don't over-estimate what power a 12 year old can exert.
Family-wise it takes two, could someone not have mentioned these pregnancies? Is there a sympathetic family member who can act as peacemaker?
MIL passed comment, did she sympathise, pitch in? If not she can't have been too fussed. Some people speak before they think. We all have off days honestly! If you had a time machine you could zip back to her house when DH was small and had d+v. Would she have everything sparkling? Laugh it off or ignore, it isn't worth dwelling on.
Hope DD is better now.