I have m.S. And from my viewpoint I know why he is feeling this way. The reason he would even think of leaving is so he won't "burden" you.
I also felt the same way when I found out, but my fiance would not have any of it. My fiance is still with me today. And to answer your question, yes, both men and women can have sexual disfunction. But that does not mean it will happen. I hope you both can work it out, I know how hard it is.