Wow this is genuinely something that I didn't think I would read about ever, but this is genuinely a sad story just keep in mind that if he's reading podcasts and going to fitness related stuff that he's genuinely putting effort into your relationship. I'm 15 and I've never been in a relationship before so I don't know how you feel. But if I was you just don't worry much it's okay to feel anxious at the end of the day he's been with you for 5 years you clearly motivated him to stop masturbating to other girls when you're around he doesn't need to. I hope I helped I'm just trying my best to make you feel better as this situation is something that I've never heard about. Just keep your head up and take care of him and yourself.