Bad stepmom 😭

I’m currently 17 w + 1 d pregnant with my rainbow baby. Before my husband and I got together, he already had a son. He’s almost 5 now and we have him every other week for a week (so basically equal time as his mom has him). Lately, I’m not sure what it is, I haven’t wanted to be around him lately 😭 I feel like a terrible stepmom. I love him. He’s my husbands light. But EVERY TIME we try talking about our son on the way my stepson butts in and makes his dad feel terrible for having another baby. We prayed and planned for this baby, months and months of TTC and it just looks like my husband regrets it everytime this little boy opens his mouth. He has shown that he is going to throw a fit when the baby comes (even said so himself!) I understand that he’s only 5 and the feeling is natural but I think my pregnancy hormones are getting to me. My husband is trying so hard to do whatever his son wants to make him feel wanted and even as a 5 year old he’s taking advantage of it 😭 He acts up all day with me and when his dad comes home and asks him why he was being naughty, he says “I’m just sad cuz I have a brother coming and I don’t want him” and my husband immediately feels bad and let’s him get away with it. I just don’t want to be around him anymore 😭