How much does fatigue,weight gain,and depression play a part in the loss of sexual desire?

I have gained about 40 lbs in the last year and a half. It has wreaked havoc on my self esteem. I also started a new job about 2 months ago. The hours are longer, highly stressful at times, and it requires a lot of energy throughout the day. By the time i get home, I am so exhausted. I have no interest or energy for sex, and this is taking a toll on my partner. I think the main problem is that I feel ugly because of the fat. He thinks that my sexual interest should always be at a high level just because I am a male.I also take cymbalta, which takes its toll as well.