Why would a guy keep another woman's number that he cheated with?

I cheated with this guy name David some time ago while he's been in a relationship. He is a cashier who I met years ago at a store where I shop I met David in 2015. And he had a hookup in 2019 which afterwards he said he didn't think it was a good idea for us to hang out again. Then a year later in 2020 he came back asking to see me again. Saying that his girlfriend was leaving the state to live her life without him in six months. And that he hoped to see me again after she left. I told him I was surprised that he wanted to see me again. Since he told me he didn't think it was a good idea. He said he didn't want to cheat and since she was leaving him he didn't have to. I didn't believe him so I didn't meet up with him again. In December of last year 2021 I asked him if I could see him again, he told me he didn't think it was a good idea. Then when I saw him again, I asked him if he still had the new number, I had given him a couple of months ago he shook his head yes. So after he rejected me in December, I decided to move on. I started talking to one of his coworkers Rick Who I befriended last Summer and in March of this year when David saw me having a conversation with Rick, (Rick was telling me how he had gone on a tour to this musem) David saw us and heard us talking and came over and stood in between us and said "how was it" and then he kneeled down acting like he was checking items on the shelve. It seemed like he was trying to be nosey so he could hear our conversation. But it doesn't make sense why he would be interested in what we were talking about.

Anyway, why would he keep my number if he's trying not to cheat again?
Why would a guy keep another woman's number that he cheated with?
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