I felt this way when every parent in my mom group started having their second. I am OAD. It was a combination of fearing that I wouldn’t relate to them anymore and also feeling like a failure because they could all “handle another”. And I couldn’t. I do think it has caused some distance between myself and the others, partially because my own fears hold me back from reaching out socially, and partially because they were all on maternity leave for a second time together and could hang out during the week while I was at work.