My boyfriend stopped going to the gym?

My boyfriend use to love going to the gym. He was training hard and going every day. We got back from vacation early August, and we worked out the day after coming back home. Everything was okey the first weeks but now he doesn't want to go anymore. He always says «no» when i ask him and he won't tell me why. Its been like this for a week. What can his reason be?

Updates
9 mo
Update: we are now good.
After asking him multiple times, I finally got an answer.
We worked on it and we are back at the gym together again.

Side note: Don’t know why girls on here always answer with such hate.
The boys (most) gave genuine answers.
My boyfriend stopped going to the gym?
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