When a man says something like this it's quite a disclosure! If he has said so before anything else has happened outside the marriage, that would be good... but often it is an excuse...

However, men are visual fellas, ok? So you need to ask HIM what would make you more attractive, to him... he'll probably mumble something like Idunno but give him some ideas... and yes, weight might be one of them...

maybe marriage counseling is still an option...