Hi just popping on quickly to give hugs, I didn’t breast feed so can’t really comment on that but he is using you as his comfort so you need to try and replace this with something else. Does he have a lovely or soft toy he sleeps with? A top of yours do he can smell you sometimes helps.
Can anyone else, partner, hubby, grandparents do bedtime for a while? Would he have a drink out of cup whilst reading a story and having a cuddle!?
With regards to the crying, try and remember that as long as you are with him you are reassuring him that your not leaving him alone and that is totally different to walking away.
Any sleep training or breaking a habit when they get older will be met with resistance so you may get some tears. Can you try some gradual withdrawal or someone else do the inital few days so that you don’t feel anxious about it!? Maybe you go out for a walk to remove yourself?x