Dear Stuart,  

The simplest answer to your question is this: you are married, that is your call. Being the best husband -and in the future father- you can is the way to heaven for you. This is what God wants you to do with your life. And being a husband means that God does not want you to be a priest, as long as your wife is living and you have children who depend on you.  

There have been cases, but they are totally exceptional, in which both husband and wife feel such a call, he to the priesthood and she to religious life, that they receive a special permission to separate in order to follow their vocations (if you are validly married you cannot be "unmarried"). But this is very, very rare.  

The reason you can't be a husband and a priest part-time is not simply because it is "against the rules", but that the "celibacy rule" is there because of the nature of the priesthood. The Church discovered from very early on, from the time of the Apostles, that the priesthood meant such an identification with Christ and such a dedication to his Kingdom, that celibacy was a gift that was given to those called to the priesthood.  

I would recommend that you direct your desire to serve God through your marriage. Growing in your marriage, supporting your family, loving and giving yourself to your wife like Christ did for the Church, serving your neighbor, building up your parish community, helping the youth discover their faith, helping out your pastor, teaching... Perhaps in the future when your children have grown up, Christ may call you to be a deacon... 

God bless.