Damn, I love a question like this. Look at all the Bitchez saying how sex isn't the most important thing, and how 'yes, you can live without sex'. He's only 50. And unless he is already unhealthy, there is NO reason to stop wanting action at 50. The problem is likely you, he is taggin' some other pieceofass, unless there is already a health problem, which you would know about. Chances are, you don't provide him with enough. A 50 year old guy with a young girl? I'm sorry, but I'd be hard all the time (instead of 90% of the time), and I suspect most guys are that way. So where else is he getting it from? And why? Likely because you stopped providing sexual release to him and for him. He's tired of putting in all the work, being the one to initiate it, making sure that you are sexually entertained, and meanwhile he gets nothing but an unenthusiastic missionary release at the end.