Which ever way you look at this, it was right to end the relationship because there is no trust on either side.
My husband had female friends when I met him, which I was happy for them to continue because I do feel men and women can be platonic friends, but I will admit there has been one who came along post marriage who I was very wary of as I felt she had ulterior motives and he was too naïve to see it - this was my intuition and I follow my intuition. Looks like you may have similar concerns.
From the most innocent perspectives your fella clearly thought you would kick off about a female accompanying them from the start and that is why he omitted the fact she was going too. Was he warranted? Only you know but he clearly didn't trust your reaction. Or maybe it wasn't innocent and that's why he didn't tell you!
Then he introduces the fact she maybe arriving mid holiday, he doesn't know yet, when she was already there, why change the lie, part way through the holiday? Did he know it would come out anyway (as it did through social media), were they egging him on, either way it wasn't really a good move was it. And his female friend was clearly egging the pudding with her comments so he clearly misjudged this situation before he went on holiday by keeping her presence quiet because she is not the discreet kind is she?
He should have faced this before he went and risked you being jealous....but why didn't he, do either of you have a track record, him for cheating or you for being controlling? Or was he judging you on his past experiences with other women and he chose not to risk spoiling his mates holiday.
You on the other hand were suspicious enough of his comments about a female friend potentially joining them to check it out on social media and discovered she was already there. Why, were alarm bells ringing?
These are not questions we can answer from the info available but it comes back to the fact that he chose to lie about the situation before he departed and didn't give you a chance to be controlling, understanding or accepting. So we will never know what your reaction would have been, but we do know he chose to lie. So no, I don't think you are overreacting.
And after writing all of this, I have just spotted that you have just had a miscarriage and he still went away? Yep, dump, dump, dump, he has no consideration for your feelings, only is own.