The fact that he struggled to lose weight when he was younger doesn't mean that he won't/can't be into it. There are certainly people who grew up chubby and worked hard to 'fit in', but who never turn against fatness, rather just hide that away as hidden desires. Not saying that desire is always a kink or fetish, a lot just, for example, marry a fat partner and let their weights drift up over the years, or just dream of that.
Obviously I don't know the case with your boyfriend, but try to relax and let him speak for himself, and trust him to be honest with you. But also maybe ask him where his desires are, regarding you and regarding himself (and obviously make sure you know where your boundaries are on what you'd want for him)
If he's not good at talking about these broad topics, maybe go into some specifics and see how he responds. There may be plenty of things about a bigger you that he could really get into.
2 years
