You have most certainly not stuffed up!!!!!
You have done wonderfully meeting your little man's needs. It's hard, I know, especially when their needs don't seem to fit in with certain expectations or what the books say, or whatever, but you're never doing the wrong thing if you're doing what your child needs you to do.
Forget about Tizzie and the crying thing - it clearly will not work for you. It is NOT the only way.
DS actually grew out of feeding to sleep around 12 months, and then would only do it ocasionally if he was really, really tired up till he weaned at around 2. So they're all different.
Some kids just take longer to get the hang of being alone to sleep - I reiterate, it does not mean you've done anything wrong. You sleep with your son and breastfeed him to sleep because that's what he needs you to do, not the other way round (if you see what I mean). You might be able to try some gentle techniques (Pantley is a great place to start) to wean him off this. I hope that you can find a way to get the rest you need while meeting your sons needs

Just for some perspective - I fed my DS to sleep most of the first 12 months. I co-slept for most of the first 20 months. I tried all sorts of things to fix our 'problems' but nothing actually worked for us. And yet..... DS now sleeps alone all night (unless sick), in his own bed, and even sleeps all night without waking for us sometimes! Sometimes I can't believe this is the same child that went months waking to feed 5-6 times a night and would scream if left alone.