I think, from personal experience, that he may have lied because he knew you'd be upset and maybe start a fight or whatever.
he lied because GUYS LIE. They lie about everything; important stuff, unimportant stuff, stuff that's obviously a lie, whatever they can lie about, they do. And I'm not slamming guys; I'm just saying from 40 years on this planet, I know they lie before telling the truth ever even occurs to them. For no reason at all. Maybe without even realizing they're doing it sometimes.
he was planning to be with the first friend, and then the second friend came along and somehow it ended up being the two of them instead of the original two. ANd he didn't think he needed to explain it to you because
it's none of your business.
Wait...are you married? No, you said boyfriend. Okay, so yeah...it's none of your business.
I'm not trying to be mean, I swear.