Weight gain

I have been resisting my fascination with large women and weight gain all of my adult life. I have tried to get my wife who is slightly overweight to gain for years without comming out and telling her my fantasy. By my converations with her I know she does not understand my desires. The feel of a soft woman is so sentual. She will not gain for me even when I tell her how attractive she is and rub my hands over her semi soft body. I have a hard time mentally getting myself to gain but I have put on about 15 pounds over 10 years. I don't want to be unfaithfull, but I have a very strong desire to be with a large soft woman. Does anyone have advise ?
17 years