Sir Chris Bonnington once put it something along the lines of :- " Mountaining I suppose is selfish, yes it is selfish, but its love of the mountains and the burning desire to be among them, that makes me the person I am. Without them I would be a lesser person."
My wife no longer comes on walks with me, she used to, but due to health problems and the resulting lack of fitness, the walks became increasingly less enjoyable. She does get frustrated at times when I go off, but knows that I have to do the things that I do. Its all a compromise, and I try to assist her in the things she wants to do, even if it means foregoing something that I would rather do. Its easy to get so enthused with activities like running and walking that it becomes an obsession. Once it becomes an obsession, it then becomes the main focus and parteners feel threatened by it, and start to resent it.
Its then only a matter of time before it comes to a head.
Good luck to you.