Oh my goodness this sounds just like me! For my first child, I rocked her to sleep! I could've kicked myself once my second child came around, but I was bartending 5 days a week and just wasn't around to even "know" what healthy sleeping habits were for her. I mean, MY sleep habits were all crazy as it was! Anyway, she was only 15 months when my son was born and I started realizing it just simply wasn't going to work. I'd rock or walk her to sleep, and then it never failed, as soon as I'd get her to sleep, my son would cry and wake her up, so it was constantly moving from one child to the other and I KNEW at that point that I HAD to have it all wrong. So, here's what I did. I know you said you have tried to just leave him to cry, but really, you didn't. IF you go back into that room before he cries himself to sleep that you have completely defeated the purpose of the whole process. I talked with my pediatrician and she said "You have to let her cry it out." So, I went home and did that, and guess what, she PUKED from crying so much! So, called the doctor back the next day and she said, "I know this is going to be very hard, but the important thing to remember is that you're doing this for your child because she NEEDS to have healthy sleeping habits. So, tonight, when she is crying, just let her cry herself to sleep no matter how long it takes. She may puke, she may not, but if you go in there because she pukes, she will puke again tomorrow night because THAT's what brought mommy into her room" So, that night, she did her usual standing up in her crib and screaming and crying until she puked, but within a couple of hours, she had fallen asleep. I went in, literally crawling on the floor because I didn't want to ruin the whole process I'd just suffered through, and cleaned up the small amount of puke on the floor. Well, the next night, she did puke again. Then, gradually over the next few nights, she got to the point that I could lay her down and although there were times she'd cry at first, she fell asleep on her own and slept through the night. I'm telling you what, those nights were HELL, but I'd do it again over and over if I had to. You can imagine how different I did things with my son. I NEVER let him fall asleep outside of his crib if I was at home. Plus, I started him in on a nap routine at 3 months, which is the same time I went from him sleeping in a bassinette in my room to his own crib in his own room. That child is the world's best sleeper I swear! I have NEVER had any problems with his sleep habits. So, start your 2nd one out the right away, we all learn from mistakes.
Now, my kids are 4 and 5, and they go to bed at 8:00 sharp. They sleep ALL NIGHT and have all of their lives (besides that first 15 months for my daughter). They wake up around 7-7:30. It's great because my husband and I have our own time just to each other every single night. I know it's helped us through a lot. We have plenty of time for talking, intimacy, or just plain relaxing together. So, do what you have to do make it through hearing him cry, but do it, you will be the happiest rested mommy in a matter of 3-5 nights from now!!!