Other woman number?

Long story short caught husband messaging another woman. (Emotional affair at least) He kept her number but says they aren’t in contact. Why would he keep it if he ‘isn’t speaking to her’? And yes, I keep numbers of people I don’t speak to but surely that’s one you’d delete? Sorry if you have seen this before not sure which catagory to post in. He wouldn’t keep it for no reason would he
Other woman number?
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