first off, congratulations! as far as your little one, what i did with mine was let him cry. right now, he knows that you will come running as soon as he cries or if he cries long enough. he knows how to push your buttons. i would start watching suppernanny. it is a GREAT show. even my 10 year old watches it with me so he can try new things with his 3 year old devil brother. lol
it will be hard to let him cry but get a pair of ear plugs, put them in, tell him it is mommies time for some peace, give him something to play with, nap time, or even an educational or fun movie and make that his personal time for him to relax. it wont happen overnight, it took mine about 2 months to realize that it was not going to work anymore but it did. you can also try a part time day care or play dates somewhere that is understanding of your situation with him. he will be fine and a little crying never hurt anyone. good luck let us know how it goes. just remember, you can do this and you will.
oh, as far as the new baby goes, let him be a part of it, shopping for clothes and toys and feeding and the whole nine yards. he will feel like the big brother. if he will sit for book time, there are wonderful books you can get. i did that with my kids. i have 2 boys, 10 and 3 and then 6 months after having my 3 year old i was prego with my twin girls that are now 2. it made a hugh difference having the other kids help. even nicholas that at the time was just over a year. good luck again, B. sahm 10,3,2,2.