Maybe try putting him down an hour earlier for bed? I know that sounds weird but that may help him sleep better at night. At this age, 6-6:30 is a great bedtime.
Alternately, have your husband go get your son settled back down if he wakes at night. (Since he can't stand the sound of the baby fussing!) There's no need for a 19 month old to be eating in the middle of the night - he wants to nurse because that's how he's been trained to fall asleep. So you need to train him to self-soothe at night, and perhaps since Daddy can't nurse him, he's the perfect person to lead the process! (And you can get some sleep, finally. =) Maybe if your son has a special stuffed animal or blankie or pacifier or whatever, that will help.
I'd recommend letting your son try and settle himself down for a minimum of 5 minutes (watch the clock) - he may very well fall back asleep on his own. I noticed with my kids that many times when I thought they were awake, they were actually semi-asleep and just making noise. If I ignored them, they'd go back to sleep in 2 minutes or so. If he is still fussing after 5 minutes, go in and without talking to him or picking him up, cover him with his blanket, pat his back, and then leave. Wait 10 minutes, and repeat if necessary, increasing to 15, 20, 25 minutes if you have to. We did this with my older daughter and after about 45 minutes the first night, she fell asleep. The second night it took about 20 minutes, and after that she slept through the night just fine. (With my younger daughter, I did this process too, but she was a newborn so it didn't take as long!)
Good luck!