I had the same problem with my oldest son. My ex was deployed to Saudi at the time, and I got into the habit of sitting with my son until he fell asleep or even letting him fall asleep in my bed and then carrying him to his.
Needless to say eventually he wouldn't sleep unless I was with him. It took several nights of CIO to get him to sleep in his own bed, during which my father (we were living with him at the time) would staunchly refuse to let me go comfort him. After a few nights the crying stopped and he'd happily go to sleep on his own after a bedtime story.
I've seen other advice regarding how to wean children off needing mom/dad to sleep, and it often involves a set number of "comfort" visits per night, consistently, with a decreasing amount of interaction until you're simply going in, patting their back or tucking them in and then leaving. I don't know if that works or not, but I'm guessing for some people it does.
Do what you're comfortable with doing. You may have to try a few different things. It is really hard to let them CIO - I couldn't have done it if my father hadn't been there to keep me sitting in my chair. :-) I'm glad he did, but still...it was rough.