Just tell him you're trying to stay vegetatian as a choice. You may not do it for ever, but maybe compromise by having 3 nights of something other tham meat or fish is a healthy choice. Salads are pretty bad in the winter - but great for the summer. Soups and casseroles are better for the winter months so offer to cook the veggie options. Try to get a few second hand veggie cook books to dip into for ideas.
Mexican is good, as is some older traditional british stuff like leek & potato soup with crusty bread.
Veggie Haggis is a favourite of mine, and anything with potatoes or pasta is filling.
Try some buffet style nights where everyone helps themselves from what is cooked. You could have the veggie option while he has the meat options.
What he doesn't want to do is end up cooking two meals every night. To get around this - buy some ready meals to keep in the freezer, so when he fancies fish - just bung one of them in the microwave - simple.
I keep a stack of vestas meals in the cupboard for just such occasions!
Make it your job to search out and buy the options you like - then keep a stock. This will get around his problem of "what will I do for him?"
The easier you make it for him, the easier will be your time of it. Plus you will get some practice in cooking for yourself.