It's wrong to comment negatively on a partner's attributes.
Jonah's partner Amy has started eating more junk food and stopped exercising which has caused her to gain a lot of weight.
Jonah wants to encourage Amy to lose weight.
Jonah invites Amy to join him at the gym and suggests cooking healthy meals together.
Jonah tells Amy that she is getting too big for him to find attractive and that she needs to lose weight if they are going to stay together.
Amy does not feel attacked and is able to build good habits with Jonah.
Amy is hurt and goes to stay with her sister for a few days while she rethinks their relationship.