Every time you pass a slim attractive lady make sure you tell your missus how sexy they look, how great their legs look, how pert their bottom is….
Seriously its a difficult topic to discuss with your other half as you never know how they will take it (i have been there). Firstly you need to reassure her that you still find her attractive.
Finding a way to exercise together is a good way to kick start a healthier lifestyle. It needs to be something you both enjoy otherwise it will fall by the wayside.