I had heard about the cabbage leaves but wasn't sure if it was an old wives tale! I may be totally wrong though.
Also, I'm not sure if drying up your milk would be the answer-a lot of toddlers will 'dry nurse' and not sure if you could get rid of your milk completely-it may make your DS nurse more as he's not getting enough milk.
I would definitely recommend joining the Facebook groups-I am not on Facebook properly but set up a profile (you don't have to use your real name) just for the breastfeeding groups.
I understand completely what you mean about other people's reactions and looking through the Facebook groups really helped me to feel 'normal'. It was helpful to read other people's experiences of self weaning and to see photos of mum's feeding their 3/4 year olds. You will probably get some good weaning advice too.
I wouldn't worry about his appetite, it's normal at this age to still be having lots of breastmilk.
At 3, he may be too young to self wean-some do but many don't until older.
I think you need to decide what you want-there may be ways of continuing that makes it easier for you. I think it's common to go through phases of thinking 'I don't want to do this anymore'. Also, be aware that there are disadvantages to stopping - you will need to find a new tool to stop tantrums,help when he's sick,possibly sleep may get worse,he may become more clingy,etc .
Not saying you shouldn't stop, just things to consider.
If you do decide to wean -
Probably how to go about it would depend on his nursing pattern now-how often does he feed?for how long usually?does he feed to sleep?feed during the night to get back to sleep?
It also depends on his personality, whether you would think he would be better with set 'rules' so no milk until after lunch for example, then no milk until after bath time.
Or you could try letting him nurse when he wants but taking him off after a minute or two so the feeds get cut down that way.
Some toddlers become quite anxious though at their milk getting taken away and can want to nurse more and more as a sort of panic response to you cutting the feeds down. Sorry, I don't feel like I'm being very helpful. There is no easy answer I don't think.