Is it legal for me to see the pictures of a celebrity and a girl in his house?

It sounds like this is an invasion of privacy that would also violate the celebrity's right of publicity. If photos were taken surreptitiously within his house this, may also be a criminal invasion of privacy, stalking, and other crimes. Depending on who owns the photos, you may also be violating that person's copyright.

Depending on the pictures, a claim for invasion of privacy comes to mind. The celebrity may or may win, but I am willing to bet that he has more money to spend suing you than you have to defend the lawsuit.

It depends upon how you got the picture. If you were outside on the sidewalk and he and the girl were in clear view, then there is no expectation of privacy on his part and he could not successful sue you [although he may threaten to do so; check with the magazine if they will provide an attorney for you or how they will protect you]. If you went onto his property to take the picture, you could be sued as you were trespassing. If the magazine is going to try to extort money from him not to publish the picture and you know they might do that, you could also be sued. Find out more about the magazine(s) you intend to sell the pictures to. If you think the pictures will be embarrassing to the person, reconsider whether you want to make money at the person's expense.