This business of -- he's no longer attracted to you because of a few gained pounds, is not the story.
The story is he's looking to pull away from you.
The reason someone would do this if there is no reason to, would be due to something on his part that he has done to you that he shouldn't have.
In other words he has probably already done something that he shouldn't have.
That would explain this kind of behavior when it doesn't make sense.
Do you have any suspicions at this point?
It may be interesting to poke around and maybe get him to confess.
And watch his eyes closely. When your on to whatever it is, you will know by the reaction in his eyes. - He can't hide it.