A lot of people on this site have written good things about the Couch to 5K program. If your sweetie is a runner, you might sign both of you up for a 5K and do the program to train for it. I bet once you start running, you will want to eat better and the weight loss will begin.
Many people when they start running, run too fast. If you can't hold a conversation, you are running too fast. Slow down. You might feel like you are just plodding, but thats okay. If you can't slow yourself down, try a run-walk combination.