My suggestion would be to let him cry himself back to sleep. Everyone needs to learn how to soothe themselves and it may take several nights but eventually he will learn that you are not coming and that he needs to find something else to soothe himself. Is there something that you use during the day to soothe him if he gets fussy? A blanket or stuffed toy? If so, try making sure that is available to him. Also, you'll learn if the cry he is emitting actually requires your attention. There is a difference between the "I just want attention" and the "I really need someone NOW" cry.
Now I want you to know, this will NOT be easy. It may feel like you are neglecting him and you will not sleep for several nights. However, in the long run, he will learn to go back to sleep on his own and you will have given him a little taste of independance.
I went through the same thing myself accept I waited until my daughter was over a year old and it took forever. When she finally did sleep through the night again, I was in her room constantly making sure she was alright because I couldn't believe she hadn't cried out for me.
You are not ignoring or neglecting your child. Just listen for the cues and eventually you'll get your full night sleep again.
Hope this helps.