I know how you feel; my son's father was the same. We had a good few months in the first year where we were having sex all the time, and then nada. I know his sex-drive was fine because I caught him looking at porn all the time.
The trick in this situation is to try not to treat your partner as the bad guy, and approach him, talk to him about it. Ask him why he looks at porn. Don't demand or be angry, just tell him you'd like to know. Ask what he gets out of it that he doesn't get from sex with you. So many couples don't talk about sex, but I'll be honest with you, I think not talking about sex in a relationship is like not talking about money; it's a problem waiting to happen.
Also, the fact that you sleep apart is not good, regardless of the sex you do or don't have; the only nights my partner and I sleep apart is when we're having serious fights; the rest of the time, we'd rather be together, even if just to cuddle or reassure each other that we're still there, that we're not angry or upset with each other. There's such an emotional distance between couples when they sleep apart; even if you're not doing anything besides cuddling and kissing, sleeping in the same bed has serious benefits.
Good luck!
His_einna