Simply put, first loves are harder to get over. He had your heart, you shared yourself for the first time with him, you built all the memories of any good relationship you've ever had with him.
I hope that you really love the guy you're with now, and haven't just stayed with him because he helped you get over your ex. When you finally do get over your ex, and you will eventually, you will be forced to take stock. Make sure you're with your current boyfriend because he's who you want, not just a shoulder to cry on... that's not a good relationship for anyone, most especially a person who is vulnerable. It's also sometimes referred to as a "rebound"- I'm sure you've heard that term before.
I still think about my first real love, and we've been broken up for over 3 years now. Granted- we also went out for over 3 years. They stay in your mind because they still feel like home... even if your heart has a new home already. You'll find your way eventually. You may also want to consider that your current boyfriend, at least on some subconcious level, reminds you of your past relationship because he was the one to dig you out of the mental muck and mire you were in. You may want to think about whether staying with him is exactly what's helping perpetuate your unshakable feelings. I hate breaking up a good thing, but you may just be clinging to the one who saved you. It happens, don't feel bad. Just do some thinking and see how your heart feels on what you think about.
EDIT/NOTE: Your last post, just above mine, wasn't there when I wrote the above. Bearing that in mind, I think you're already heading in the right direction- I think you're in a very unhealthy and self-perpetuating problem with this setup. There are plenty of other good guys to take care of you. You may have to walk away from this situation. It's only going to keep hurting you.