I THINK YOUR SON IS STILL GOING THROUGH THE TERRIBLE 2'S, WHILE ALSO GETTING USED TO BEING A BIG BROTHER.  EVEN IF HE IS GOOD WITH HIS BABY SISTER,  THAT DOESN'T MEAN HE DOESN'T GET JEALOUS OF HER.  MAYBE YOU COULD SPEND SOME "SPECIAL TIME" WITH HIM BY HIMSELF.  SEE IF SOMEONE YOU TRUST CAN MIND YOUR DAUGHTER EVEN FOR AN HOUR.  ALSO, MAYBE YOU COULD LET HIM HELP WITH HIS LITTLE SISTER.  E.G. GET A NAPPY OR TOY FOR HER,  OR HOLD HER BOTTLE WITH YOU WHEN YOU FEED HER.  I DON'T HAVE ANY BOYS BUT I HAVE 4 BROTHERS AND 3 SISTERS.  APART FROM MY YOUNGEST BROTHER, WE WERE ALL JEALOUS OF OUR NEW BABY BROTHER OR SISTER.  THIS IS HOW MY MUM HELPED ALL OF US GET USED TO THE NEW BABY.  GOOD LUCK

I am no expert but i would have to say your sons probably feeling a bit out of sorts because he is no longer everyone centre of attention. While he doesn't seem to blame the baby for coming into his life, i think that he might be having trouble with the people around you now taking more notice of your new born rather than him. I am guessing that before your little baby girl came along your son use to get alot of attention from the people around you including your partner. If you have a word to the people around you about this problem, i'm sure that this can be sorted out. I don't think it would hurt to try to give him a bit more attention than they have been since the baby was born. I would try this and see if it helps, it can't hurt. Good luck.

My son, has just recently stopped doint this anti-socail behaviour.  I just ignored it, I found the more I tried to get him to talk to people and pushed the issue the worse he got.  So I would just say to people he's not talking today, or he's going thru a stage.  Most people were understanding.  It will pass with time.  Even though he loves the baby he maybe feeling a little left out from the extra attention she gets from everyone and this is his way of getting somne attention.  You could try and have some special time just the 2 of you, or special dad and him time.  see if that helps.

As for him running off, as someone else said get one of those leads, you put on your wrist and theirs or the little backpacks witht he leads.  When my second was born I had one on my older one all the time near roads etc, because they just run off, and with the baby and shopping you can't always have a grip on them,.

Good luck, hope all goes well.

Ok with the behaviour I cannot help you, but in regards to him running off, You can get a child harness to put on his back and it can loop round your wrist. I recently wrote some advice on this subject. You can get different shapes and colours like a monkey or a dog or a poodle etc. This way you still got 1 hand free and your son can't go to far. They also have a tiny pocket in the back which can fit a small toy or something in it.