You may need the help of a therapist. Or a relationship coach... communication between you on this intimate topic is blocked... the reality needs to be addressed head-on. You're not happy and he's not talking.
Examples of what could be discussed; What's missing for you, and for him?
What turns him on? You?
What is romantic to you? Him?
Fantasies? Secret needs/desires?
Some men have needs or fantasies that are about visual turn-on's, or "dirty-girl" behaviors that are not what is waiting for them day in and day out.
Women need connection, communication and romance, to be sexually attractive and attracted right? Often this is not something that comes naturally for a guy unless someone important to him modeled this behavior when growing up.
Face it, neither gender is very good at discussion our sexual needs, there is no training for this in schools and most families never discuss sex at all.
The amazing popularity of 50 Shades of Grey may not be so amazing after all; it has tapped a wide-erotic nerve in a lot of women and men too.
And yes, he may be interested in another... and is afraid to tell you, or is lazy-comfortable in the situation of your live-in agreement. Hard to discuss this with honesty without professional help.
Wishing you the very best in your relationship,