A.F.
Hi A.! I went through this when we brought our baby girl home. My sweet, compassionate, loving, secure son TOTALLY fell apart!
We felt so bad about disciplining him for his behavior because we thought, "His whole world just fell in, we can discipline him now!" But the reality is that kids feel loved when they have boundaries. We always showed love to our son, included him in every part of our day and spent one on one time with him so we knew he wasn't feeling neglected. As soon as we re-introduced consequences for bad behavior (consistently) he was back to NORMAL!
Boundaries are such a safe thing for kids. Be consistent with whatever discipline your family uses and have lots of one on one time!
Congratulations on your new baby!