I wouldn't be concerned. He'll learn eventually and you don't have to make him cry.
I can tell you what worked for my daughter although it's not quite working for my son (he's 20 months like yours). We started with naptime. I started a routine involving books. The previous routine was lay down in her toddler bed, pull up my shirt, nurse to sleep. ;) It ended with reading books, then nursing to sleep. Once that was in place, I experimented with nursing and singing the ABC's and trying to stop when I was done. And I also tried counting out loud. But, it wasn't working and just made her anxious. Finally, I told her I was going to let her nurse for 5 minutes and then we'd read until she fell asleep. I probably offered her a sippy if she needed it. So it was read our books, nurse for 5 minutes, and then read until she fell asleep. I basically nursed her long enough for her to get really sleepy so she wouldn't protest too much when I switched back to reading. Then I decreased the nursing time....probably to 4 minutes, 3 minutes, 2 minutes, 1 minute, 30 seconds, 20 seconds, 10 seconds, 5 seconds, 1 second. I did each of those times for a week. So it did take about 2.5 months. It was worth it though because weaning her was very non-traumatic and gradual. She was really big on nursing so it worked for us. I found that as she learned to go to sleep on her own for naps, bedtime became easier too. I did the same thing for bed time, but started the weaning a little later so when I was nursing 2 minutes for naps, I was probably at 4 minutes for bed time.
With my son, I'm having trouble nailing a routine. Part of the problem is he likes to rip the book out of my hand when I've only read a few pages and insist on nursing. And at night he'll nurse and then pop up ready to play. So he's not at the point my daughter was at when we started. It's weird since he's not reliant on nursing for comfort and such like my daughter was. We'll figure it out though.
My husband was no help at all in weaning, but another idea is to alternate putting him to bed with your husband. He'll learn to fall asleep sometimes without nursing which will make weaning easier.