Take a deep breathe and don't worry, each new stage in your baby's life takes some adjustment. You haven't done anything wrong, but now you are ready to move on to a new stage. Even grown-ups have an adjustment period when life takes a turn - expect that your son will react when his expectations aren't met, but you are the adult and you get to decide what isn't working for you any more and make a change. I didn't wean my third child until she was 23 months, so I know from experience that an older child is a little bit more upset by weaning, but he will move on given time.
My advice is to do it gradually, but with a deadline in sight - maybe over the course of one week. Start by eliminating feedings until you are just down to one (which it sounds like you have done already). Then stop the last feeding. You can hold him and comfort him. Talk to him and reassure him that he is a big boy now and that he doesn't need to nurse. Be loving but firm. Since it is in the night, substitute a diaper change or a sippy cup with water, put him back in his crib and leave. If he cries, wait a few minutes go back in reassure him and leave again. He will learn that this is the new way. If you are comfortable with letting him cry for longer than a few minutes try letting him "cry it out". Tell your husband what you are doing and set his expectations for what it may be like. You may not get much sleep - but it will only be for a night or two until your son adjusts. These stages don't last forever, it can just seem like it when it involves precious sleep. Our saving grace is that children at that age have short-term memories - after a month he may never remember nursing at all or his requests will be less frequent and less intense.
After three kids I finally stopped living in fear of tantrums or tears. Trust that you know what is best and don't be afraid of how they will react. They have very little control over their world and it is frustrating for them - acting out is the only way they know to respond. You can start giving him tools to express himself - through words - in a way that doesn't manipulate you and that you can in good conscience respond to. Responding to crying teaches them that crying is a good way to get what they want. Teaching them to ask and say please before you can respond teaches them to ask and say please.
Two months after my daughter weaned, she bonked her head and came crying to me, threw up my t-shirt and latched on - wow, that was weird!! Not knowing what to do I asked her, "want some candy?" She let go and happily accepted a lollipop instead. Such strange little creatures. <lol>
Bless you - you are doing a great job. You will get through this AND he will be ok.
D.