How do I get my boyfriend to lose weight?

im wondering how I can get my boyfriend to start exercising. when I first met him he was really into exercising and was really buff! we have been dating for 3 years and he has been slowly gaining weight mostly due to his new job and long hours. I've tried dropping hints about how I liked how buff he was and I've even tried the tough love approach but nothing is getting to him. he complains a lot about being fat but does nothing to fix it. I wouldn't mind working out with him but we have different work schedules! how can I get him to start exercising without hurting his feelings? HELP