I THINK IM LOSING MY MIND?

Some background information would be that ive been dating this guy for almost 4 years.We live with his parents as he has multiple degrees but cant find work with this economy. I didnt want to live there but he wanted me to be with him, so i did. Recently our relationship has taken a turn for the worse. I dont know if hes depressed but hes not into our relationship or into me i feel like. I feel the conversations we have are not boring, but not what id like them to be. I feel as though our sex life is non existent and when i mention things he will blame it on being tired (he works a seasonal job while looking for a real one) or he will blame it on possible low testosterone from smoking. I know hes not happy living there or with the job situation but i dont know how much longer i can stay with someone that makes me feel unhappy in my relationship and sex life. I dont want to leave him but at the same time i feel like i deserve much more. I work a steady job for a neurosurgeon and not to sound conceited but im a 25 yr old good looking and in shape woman. I get looks and hit on constantly by other men but i feel as though my boyfriend doesnt even see me sometimes. i dont know what to do, i keep going back and forth in my mind but at the same time i find myself getting more and more confused. Sorry this is so long, i just i dont know what else to do anymore.