My husband suddenly fell in love with fitness and went to the gym after work. Is it just fitness?

I don't know. If you are worried, you can set up a simple gym at home. If his purpose is to keep fit, he won't go to the gym if he has a fitness machine at home, or buy a multi-functional treadmill, so that two people can communicate more while exercising, so it's not hard to understand whether he is thinking about it or choosing an expensive one, buying Lin Kang John Lone series and high-end machines. He is reluctant to leave such expensive things at home, hehe.