Sexually stuck

I’ve been in a great relationship for about a year and a half. I love my girlfriend, but I don’t really want to have sex much. I work a lot (a lot) and at night I’m exhausted and just want to go to bed. When we don’t have sex my girlfriend often cries and says that I don’t desire her anymore, and that breaks my heart and makes me feel as if I’m a bad boyfriend or deficient in some way. I really want to want to have sex and I really want to fulfill her needs and desires in this relationship. I figured that it was just my work schedule and the fact that I don’t like most of my jobs, but recently I’ve been out of state on a more artistic job. I’m surrounded by absolutely stunning women, a few of whom have come on to me. I politely told them that I have a girlfriend and we’re all still friends, however there is one woman who I am completely and viscerally attracted to. I can’t explain the attraction, but I find myself completely drawn to her, and it’s clearly reciprocal. Nothing has happened, but suddenly my sex drive is back and I find myself fantasizing about kissing this woman and sometimes more. Sooooo. I feel like shit, but it makes me wonder if my relationship isn’t working out. Part of me really feels like jumping ship and running away with this other woman and part of me says that if I do this situation will just repeat itself a year from now with a new “other woman.” Basically I don’t know if this is a sign that my relationship is on the rocks or if this is fairly par for the relationship course. Any help is greatly needed and desired.