If my boyfriend had a female staying over and was hiding it from me, then yes, I'd be mad. If he told me a female friend was crashing at his I wouldn't care (unless they were in the same bed, that is a no-no), but the fact he is hiding is a bit dodgy.
However, from the wording of the text I wouldn't be worried about cheating, I'd just be mad he hadn't told me about it.