Where Do I Begin?
It really depends on what role you are playing in this process. It doesn't matter if you're the husband, wife, father, or mother, nor is it affected if you are straight, gay or transgendered. If you are the one who wants to end the relationship, you are the moving party. Your soon-to-be-former partner is the nonmoving party, whether they want the breakup or not.
It's especially true for the moving party that s/he is certain this is the right thing to do. That may mean real soul-searching on your part. Or it may not. If you've been uncomfortable, bored, disinterested, or turned off for a while, you may not need to reflect very much. And if you've already found another person who rocks your boat, in your mind you may be already out of the relationship.
Some people slide right from total lust to feeling nothing without even noticing it. One day they wake up and realize they don't know the other person in the bed. It's pretty hard to reverse that final emptiness with therapy or counseling. (Don't even think that having another child would do it. The odds are highly against it and you would be doing a disservice to your potential child.)
Others see signs along the way but may misread them or be at a loss as to how to handle them. Depending on how far along you are, you still might be able to go to couples counseling, or even individual psychotherapy, to see if the coupledom you are in is past its sell-by date. So take a good look at you and your partner and, if you think there's any chance of rescuing the marriage, go for it.
On the other hand, if termination is the only option, then both the moving and nonmoving party should assemble their committees, people to bounce ideas off of, to turn to for support, and to tell you the truth even if it hurts. No one does well going through a divorce alone. Everyone needs a friend in their corner.
But beware! Membership on that committee is solely up to you. Do not let anyone put themselves on it. That means your mother doesn't get automatic membership, not unless you want her. And keep in mind that membership is at your discretion, and you may remove people you feel are not helpful. Your committee is there to help you, not tell you what to do. Be strong on this.
If you're the nonmoving party, you should make every reasonable effort to try to persuade your partner to change his or her mind. But notice the operative word is 'reasonable'. We've all seen movies where a spurned spouse uses the threat of disinheritance or loss of access to a beloved child to try to force a leaving love to return. It makes good stories but rarely leads to a healthy reconciliation.
Once, a divorce could be thwarted by one party refusing to agree, but those days are long gone in our country. Kenny Rogers sang it clearly:
You've got to know when to hold 'em. Know when to fold 'em.
Know when to walk away. And know when to run.
So if you know the connection between the two of you is pretty much severed, you need to brush up on your negotiating skills. It's essential that both of you end your relationship with dignity, and with the sense that neither of you lost all.