This was the hardest part of going from one to two. My DDs are 21.5 months apart, so about the same age difference as yours. My older one was also one that wanted LOTS of attention. Please know that it WILL get better, it'll probably take you a couple of months for things to settle down, but that's okay. Some things that I ended up doing:
1. The new baby just didn't get as much one-on-one as the first baby did. I'd put her down and let her sleep instead of slinging/holding her. I also used the bouncer seat much more, but then I could interact w/ both of them at the same time without baby on my lap. Give the older one some time on your lap, too. He's still a baby!
2. Nursing, I know we are supposed to nurse on demand, and I completely agree w/ that. But, with my first every time she cried I popped the boob in her mouth, the second child I sometimes tried other things instead, like just talking to her, slinging, bouncing, ect. Durring nursing times I'd start a movie for the older one, she'd just started kinda watching TV at that age. (and no I'm not a big TV advocate, but we are talking survival here!). Also keep a snack and drink out for the older one when you nurse, just make it a habbit to have him a snack incase he asks.
3. Give the older one specific ways to help you do certain chores and let him know how much you appreciate it. He can bring you a burp rag, diaper or even just make faces at baby while you change diapers. Giving him a 'job' will keep him more occupied and out of trouble.
That's all I've got! I know it's hard, but like I said it does get better. I remember crying and I know several other moms who say the same thing, it's hard b/c you now have to spread yourself between the two kids, and still manage the house and all that. I remember nursing baby in she sling and wiping the other one's rear! UGH! Poor baby was barely hanging on, my boob was streatching and the toddler was making a mess! It happens, but it will be over before you now it! My two are now 2 and 4 and the best of friends. Try to look at what this new baby will BRING your DS, and not what the new baby has taken away from him. It's hard to see that in the beginning, but in a few short months you will see the bond between them grow and know that they have a special gift of having a sibbling