I agree with Phil all the way on this..

My two cents:
Get fit. No excuses. Eat right, exercise more, do it for YOU not for other people. You got to love yourself man.
Sort out your relationship. Either end it, or make it work. Talk to her about things, she might feel the same way.
Stop worrying about things like your age and running out of time and going through a dry patch. Sex isn't everything in life. Get single, n if ur struggling, get help on this site