BornToFly, I could have written your post almost word-for-word!
That being said, I can't offer any advice about how to fix it because I am in the same boat, unfortunately. All I can say is just try to be happy with what you have, and don't dwell on what others have (and that you want).
It's easier said than done sometimes, I know. Especially when things like weddings and babies come along. Sigh.
It's hard to put on that happy face for someone else who is happily parading around with what you want (and can't seem to have).
All I can do is go on with things and be happy with what I
do have. For me, that means being happy with the freedom I enjoy --there's no one to be accountable to but myself for anything. I can go anywhere and do anything I want at anytime without checking with someone else about it. I am happy about the friends and family I have who I can share good times with. I am happy about having a good job, a home of my own, and so on.
Maybe someone will come along for me one day, and maybe no one will. Maybe it's just my lot in life to go through it alone. Who knows? All I can do is keep living my life, be happy with the things I do have, and keep my eyes out for that tall cowboy on the horizon.