“I’m always the one who has to apologize.”  She says. “What?  You never apologize!  I can count on one hand how many times you’ve said you were sorry.  If anyone in this relationship apologizes it’s me,” he replies in indignation.  They are looking at one another as if the other were an alien living in an alternate reality.  Why?  Because they do live in separate realities and we don’t remember what was said.  We remember what we heard.  Write this down and post it on your fridge.  We don’t remember what was said, we remember what we heard.  That’s the only reality that matters.  So why doesn’t this couple have memories of hearing “I’m sorry” from one another?  Because no one ever taught us how to apologize.  We heard as children, “Tell your sister you’re sorry!” from Mom, but that’s all the instruction most of us received.  Follow the below steps and I can guarantee your spouse will not only forgive you, but remember that you said, “I’m sorry.”
Step 1.  Take full responsibility.  It sounds like this.  “I take full responsibility for my behavior last night and there’s no excuse.  It was out of bounds and you deserve better.”  It is tempting to add excuses to minimize your responsibility; don’t do it.  Additionally, if you add a “but” then you are no longer taking full responsibility but are sharing responsibility with your partner.  Even if that’s completely fair, don’t say it, regardless of what your partner may have done.
Step 2.  Show that you “Get It”.  It sounds like this. “I know that raising my voice and snapping at you must make you feel like I don’t respect you.  I know it probably even scares you when I do that.  I would never speak to anyone else that way so it must come across as a lack of respect or love for you.  I get it.”
Step 3.  Express remorse and regret.  It sounds like this.  “I hate that I hurt you.  If I could take it back or have a do-over, I would in a heartbeat.”
Step 4.  State your specific plan to minimize the chances it will happen again.  It sounds like this.  “Next time I feel myself getting that angry, I will ask for a time out and go calm myself down.  I won’t let it escalate to verbal abuse.  I will remind myself that you are not the enemy but instead someone I love.  And if that doesn’t work, I promise to get some help with managing my anger”.
Step 5.  Offer to “make it up to” your partner.  This one is easy, it sounds like this.  “How can I make it up to you?”  If your partner doesn’t have any ideas then throw some out there.  “How about I take you on a proper date and I will do all of the planning.  I’ll even find the babysitter.”
Step 6.  Ask for forgiveness.  It sounds like this.  “Will you forgive me?”