Huge hugs! Your posts reminds me a lot of my family situation, especially after the birth of our second. It hit us all hard dh wasn't himself and ds almost 3 at the time became resentful of us but was smitten with his new baby sister but was acting out big time. Dh and I fought so much but for us it was just trying to adjust to our new family dynamics and with time and experience we got back on track.
He also could be depressed or any number of things stressing him out, hopefully he lets you in soon and it's something you can work on together good luck.