Dan's got a couple of great posts on Christian decision making and the view advocated by Henry and Richard Blackaby. Here's the links, they're long but worth reading.
I wanted to add to Dan's comments a couple of other thoughts.
Firstly, it is quite possible to be so nostalgic so as to be sinning. It is one thing to reminisce about moments long ago, but it is quite another to look back longingly at the past, or wonder "what if" especially as it relates to marriage, relationships and sin. To recall sin fondly is
a sin in itself.
Secondly, where you are right now is where God foreordained you to be and He has tasks for you to do there. We've all heard missionaries give their spiel and we all left from church feeling like perhaps God is calling us to the missions field (or at least to give money.) It is quite possible that God is calling you, however, if you are married, have kids and other responsibilities, it is more likely that God HAS called you to a missions field already and you're just not aware of it. As a believer your first responsibility to is glorify God and enjoy Him forever... and perhaps the second is to love your neighbor as yourself ala the 10 commandments. Now, your neighbor, as a married person is your husband/wife. As a parent your neighbor is also your children, and from there those near you. They are your missions field.
Many of you may have heard this before, but consider, your love and care of them is as important in the economy of heaven as the work the missionary does. Taking care of your home, your family, your neighbor is fulfilling the Law of God.
Some folks may think "well, gee, I enjoy spending time with my family... that can't be the kind of sacrificial action God demands of missionaries", but consider that God has given missionaries a heart, a joy, to be missionaries and He has given you a joy to be salt and light to your family and friends.
Lastly, we must shake off this gnostic idea that pastors, elders, missionaries and others who do more visible service in the kingdom are somehow more holy or worthy of reward than the man or woman who washes her family's clothes and prepares them meals. Gnostic dualism creeps in easily through our society and even religion and causes us to doubt not only our worth in the economy of God but also our salvation.
Salt and light.