E.T.
I know exactly what you're going through except my son has a thing for my arm. Still does and he's almost 6! He's always rubbed it when he went to sleep. I used to lie down with him in his bed and finally had enough. He never liked his crib so he slept in a double bed starting at about 13 months. For his 3rd birthday we let him pick out new bunk beds and that's when I started making him go to bed by himself. Every night, he would pick out what stuffed animals he wanted in his bed and arrange his pillows just how he wanted them. He slept with a night light and some nights he would choose to look at a book in bed after I left. I would tuck him in and kneel by his bed for just a few minutes so he could rub my arm then leave. It took a few nights of him coming out and us having to put him back, but eventually got the hang of it and now sleeps perfectly. He is still attached to my arm though and when I tuck him in he tries to rub it as much as he can, but now it's only a few seconds. It's definitely not easy when it's a part of you that they are physically attached to and I made a point not to let happen with my younger son! Good luck!