This is a great, heartfelt post, and it echoed my own emotions in a lot of ways. You're definitely not alone in this struggle.
At church, I am the unofficial head nanny, and I love spending time with the kids just as much as they love playing with me. As we got more children into the church (we went from zero to a small horde in about a year), I thought some of my ache for a family of my own would go away. I think it just increased it. Every week I see young couples interacting together and with their children; I get to teach, pray for, and cuddle little ones. It's a beautiful experience. Something I wouldn't give up for worlds, yet...I come home from church absolutely exhausted and emotionally drained. Sometimes, I cry myself to sleep on Sunday nights from sheer emotional pain so tangible it feels like a presence. I want to be married! I want to have a family! And I'm not, and I don't.
This is not my normal state of mind. Like you said, life is very sweet. God is good and He is able to sustain. He will never leave or forsake his own. Recently, with my older sister reaching forty and no prospect of marriage (even though she's had the desire to raise a family and has been praying about it since she was a young teenager), I have finally come to grips with the fact that I may never marry. I have accepted that and am at least cognizantly ok with it. I am living the single life and enjoying it! My emotions, on the other hand, are still a work in progress, and the discontent often resurfaces if I let my guard down.
When I came to grips with the fact that I might never marry, I felt I was finally able to truly pray that God's will would be done. That's not to say that I don't remind God of my desire to be married, or share with him my struggles with contentment, but I'm finally OK with him being in control. That, in my life, was HUGE!
I don't think there is anything wrong with having intense desires for something in life. It becomes wrong when you want it above God's will, with an idolatrous passion, or with feelings of envy towards your neighbor or discontent with your own lot.
I will be praying for you, dear sister! God has a perfect plan for your life--your singleness, your possible marriage, even the desires and pain you are going through now. They're all part of his plan, and nothing can happen outside of it.
Ok well...long post and I get to the end of it and realize I didn't even answer your questions or give any advice! Sorry about that!