Why do men never mention they have a girlfriend?

I’ve been mates with a guy for quite a while.. recently we have been flirting with one another a lot and chatting on the phone a few times a week etc Then a friend mentioned he has a new girlfriend so I took the opportunity to ask him and he was very casual about it saying ‘it’s new it’s going well so far but I’m very cautious haven't been in a Relationship for a while so taking it easy, told her what will be will be etc’

he never mentioned it before so feel a bit cross.. it feels like he’s led me on a bit…

he’s coming to visit me in March (lives in a different place) and he’s apparently told her she will have to deal with it …

why do guys do that?

Why do men never mention they have a girlfriend?
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