We tried to get rid of my son's paci at 18 months, we cut the end of it off so it didn't have any "suck" to it. We went through exactly what you are describing. We caved in after 10 days and gave it back to him. Then a couple of weeks ago, right around 21 months old, I started talking to him every night at bedtime about what a big boy he was, and that paci's were only for babies. I did this for about 5 days. And every night before he went to sleep, I would ask him if he wanted to throw it in the trash, he always said no. Until one night about 45 minutes before bed we were in his room and I asked him again, and he said YES! So we took the two out of his crib and he went over and threw them away. He has never asked for it since, and we did not go through what we did the first time and what sounds like you are going through now. Maybe the trick is to let him be involved in the decision, and let him decide when he is ready to part with it. My son also was down to only having it if he was in his crib, maybe start with that step if you haven't already?
Good luck!