You need to make it an absolute red-line in your life. You wouldn't go a day without cleaning your teeth, and you wouldn't do another hobby instead of cleaning your teeth - make exercising like that.
I exercise every day, and I think that's actually a lot easier than exercising five times a week, allowing you to pick which days you exercise or not. You can't kid with yourself that you'll exercise tomorrow if your routine is to exercise every day. Sometimes I get back from work at 11pm and I'll still drag myself out for an hour's run.