Hi Nicole,
There's no way to know why he's doing what he's doing unless he tells you or you find evidence of what he's doing outright.
The porn can be there because he has a porn addiction that has spiraled to this place, he might be a cross dresser for kicks, a guy with gynandromorphophilia, or a full blown autogynephile.
I can only say for certain - I'm so sorry this has entered your life. I am sure it's causing tremendous confusion for you and great distress.
Best to you.
* Autogynephilia is defined as a male's propensity to be sexually aroused by the thought of himself as a female. It is the paraphilia that is theorized to underlie transvestism and some forms of male-to-female (MtF) transsexualism.
** Gynandromorphophilia (GAMP) is attraction to gynandromorphs (GAMs), who are natal males with both breasts and a penis, colloquially known as "she-males."