How should I react if my boyfriend says a woman has asked him for a date?

We've been in this relationship for nearly a year. It's sweet and savoury. However, a girl has just asked him out and told him to go on a date. He says he has told her that he's in a relationship but that girl wants him to still meet her for once because she thinks our relationship isn't that serious (we're not sure whether we can marry each other) and I'm not that great so she wants him to reconsider stuff. They have a date now.

He told me these things. For a few days I felt there has been a third one on scene but didn't have any real grounds. However I told him that we can break up if he wants but he says he doesn't want to. And that he would just go on the date and tell her that we're close.

I've no idea how to react to this. And I don't know why he wants to clear things up for her. Does it matter what she thinks?

Could you please give me advices on how to react?

How should I react if my boyfriend says a woman has asked him for a date?
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