Guys, girlfriend living with a male roommate? Would this be a problem to you?

I have been living with this guy since 2014. We feel comfortable as a roommate so we decided to move in to another place together because the previous house owner was an asshole. My boyfriend just found out that I moved in with the 'same' roommate and he begins to feel suspicious asking why would we move together.

We used to have this girl roommate with us but she has moved to different city due to her work location. Now, he is asking me why didn't the 3 of us move in together rather than only the two of us. Do you think he has a reason to feel unpleasant?
Guys, girlfriend living with a male roommate? Would this be a problem to you?
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