How to apologize sincerely for harsh words spoken to the most precious person you know?

I had a terrible fight with my girlfriend last week. I told her words that I am so regret been said.

We are over it and fine now but I am feeling like these words are still in the air and I don’t like myself saying them to the most important person in my life. I admit I was very nervous and I spoke out loud and garish but it still bothers me. I do not want that to happen ever again.

How to forgive my self? How to control myself in the future never saying them again? It is like I had no control over my mouth when I disagree. I don’t like myself being like that. Everybody knows me as a nice person, so why it happens? How to control it?

Please advice.