K.B.
My son was doing this about the same age. The time I was spending sitting by his bed at night so he could go to sleep was also lengthening greatly. First I got him to fall asleep without me in the room. This took a few weeks as I didn't want to cause too much stress to him. I would, each night, sit or lay further away from his bed and closer to the door. After about a week I was on the outside of the door with the door half shut. After two weeks we had it down to I could just walk out of the room and shut the door almost all the way. This part didn't take any longer each night than me sitting right by his bed. So no extra time length in the routine.
The next part took a little work on my part. I let him get use to falling asleep on his own for a week and continued to let him come in my room. Then I decided to stop that also. Every time he came in, I walked him back to his room and put him back to bed. I made sure that he was comfortable, didn't have to pee or need a drink. Since he was already to the point that he didn't need me in the room to fall asleep, I could walk back out of the room before he was asleep. Sometimes I would cuddle with him for a little bit in his bed--but that's his bed and only he can sleep there so he would kick me out. :) It only took about 3 nights and the multiple trips back and forth stopped.
Best of Luck!