You’re caught flirting with your ex and don’t remember it. WYD?

“I drank too much on New Years Eve and I must have talked to my ex for about 20 minutes after my girlfriend went to bed. I don’t remember any of it, but my phone shows that she called me. My ex has hinted that she wants to get back together but we broke up for a reason. My girlfriend says I was flirting hard and suggestively on the phone. What can I do to fix things with my girlfriend who’s now concerned?”