I have posted about this before (namechanger)
Am married to an older man, we have a fantastic life, and are mostly very happy.
His sex drive has always been lower than mine, but over the past few years it has got worse. Honestly at times I think he wouldn't be bothered if he never had sex again. 
Problems are made worse by the fact he has erection problems, and therefore the times we actually do have sex it's very difficult, and usually ends up with self/mutual mastibation.
I find myself lusting after random strangers, fantisizing about proper long steamy sex sessions, as opposed to embarrassed fumbles every couple of months.
We have spoken at length about it, he is embarrassed, it's a vicious circle though? He isn't prepared to do anything about it, and each time we talk he promises to make more of an effort, but it never happens. I just want to be wanted, to make someone arroused?
The thought of being like this for another 30 years kills me, but what's worse is that I know it won't be like this, it's only going to go down hill.
It's got to a stage where I know I wouldn't feel guilty fucking someone else, but I know that if Dh found out our marriage would be over, and that's the last thing I want 