Next time don't say Sorry

I want to apologize for my behavior.

I want to apologize to my girlfriend for letting her down when I should have been more supportive.

I owe you an apology.

I Apologize, it was an honest mistake.

Oops! My bad!

I regret for any inconvenience caused to you.

It was a mistake.

I sincerely apologize for ...

I'm embarrassed.

I'm ashamed of my misbehavior.