Don't beat yourself up. You are just lucky that he was able to sleep through the night so far. Most babies his age DO NOT sleep through the night. Moms will often brag about finally being able to get their kid to sleep but usually that lasts for about a day or so then their babies wake at night again. By then, the mom usually doesn't admit that their kid is waking again because she bragged so much that he/she was finally sleeping through the night!
Sounds like 11:30 is pretty normal. Do what you have to to get him to sleep at that time. It's still reasonable for you to nurse him at that time if need be since you can still get back to sleep. If he wakes in the wee hours, you might consider night weaning at that point, just not the 11:30 feeding. It will not create a bad habit. Once they start getting more calories from solids (at about 1 year) they will not need to nurse as much. I nursed my son to sleep (still do) and he learned to sleep through the night fine (he's 15 mos). As far as cry it out, technically, their memory cannot process this type of "learning" until much older. Whatever they learn by crying one night will probably not carry over the next night. My son also cried forever (45 min?++). I tried to CIO for about 1 week +. Yes, it worked for a little while, but then he started getting in all his teeth so his sleep went out the window! Back to square one. At that point, I decided I didn't want to do the CIO thing again. Yes he does cry at times, but usually only for 1-5 minutes before settling to sleep. If he doesn't settle by then, he won't. My husband will then go in and lie down on the floor next to his crib, sing to him, rub his back, etc. When he was 6 months if nothing worked I did nurse him back down.
You can try some homeopathic teething tablets called Humphrey's. You can get them online or at Merz Apothecary in Lincoln Square. He might be teething and you don't see anything yet. This might explain why the nursing helps (massaging the gums). Don't let yourself feel like a failure for not having your baby sleep through the night. There are so many factors that affect sleep the first year, there's no way you can know them all!