How do I ask my husband if he is gay?

My husband and I have been married for a year and a half and we have a 4 month old son together. We have never really had much of a sexual relationship, when we do have sex he is distant and rarely climaxes. I have found SEVERAL times pictures, emails and text messages between him and other females with nude pictures from each party but recently he had been responding to craigslist personals add to transsexuals. In one email to an add he asked if they could meet up and he sent them pictures of himself. I don't know how to confront him about this without making him feel like im attacking him. I don't know that I want to continue with our marriage but I don't want to make him feel ashamed for his sexual orientation. Any advice would be great...