I think it is an age thing too, but what you are describing, while frustrating does sound normal. hun. I remember how hard it was. It's like you have to prove you love them.

My DD wasn't great either at first and it has probably taken her the better part of 10months to get better.

She was 2 and 10months when DS was born and was a great help - but some kids just aren't into that.
What helped was me giving DD some time on her own away from the house and away from the baby.
Playing with other kids helped as well. Do you go to playgroup? Does he go to CC?
DD really looked forward to her daycare days. I found that she was more independent the day after CC...and then it went downhill until the next week.
DOes he choose what to do? Do you reward him when he does play on his own? Are his communication skills good enough for you to explain to him that you need some timeout?