Hi D.~
This is a tough topic b/c you'll get all kinds of advice, but nobody is actually in your shoes right now but you! I agree that crying it out isn't a good idea b/c not only is it not working for your little guy, you certainly can't relax and sleep if he is crying. Certainly there is a difference btwn fussing and crying, but it sounds like your guy is all out screaming. I don't agree that sleeping with him will help you get any rest, and you'll just have to break the habit later, delaying not solving the problem. I like Carleen's advice to leave the room if your little one can understand "be right back" and stretching it longer and longer. Also, giving him a distraction like a flashlight or a kids projector might help him play until he is sleepy. The gate on the door will help keep him in his room but not feel locked in, and if you empty his room of all toys except a few that could be allowed at bedtime, you might distract him from crying. That assumes you would put him in a toddler bed, though, which might be what you have to do. He'll have enough freedom not to cry for you, and he will go to sleep eventually, even if it is on the carpet (which won't hurt him a bit). A few days of it and he'll get the idea, and even get into bed when he is about to fall asleep. Most importantly is routine! If you don't already, make sure there is a bedtime routine in place and bedtime is the same every night. Also, I have found that if my boys don't get enough sleep during the day, they don't sleep well at night! Despite what you would think, overtired babies dont sleep well. Typically, a baby can only stay up about 2 hours at a time before they need a snooze! (Yes, I know, my first was the exception to that rule and almost never napped.)
Good luck to you and I hope you find a solution. I have done a lot of research on sleep, and am the proud mommy of 2 incredible sleepers so feel free to msg me!
~L.