Your boyfriend may be joking around about your weight because he wants to wrest some form of control and power in his life.
He may be doing this consciously or unconsciously.
It is not unusual for a person to come to a point where they feel somewhat powerless in society.
This can occur quite often in life and can cause subtle to brazen shifts in behavior.
They may feel like they are not quite on the level of everyone else.
They may feel to some extent that they aren’t where they are supposed to be in life.
This causes a sense of powerless on their part.
As a result, they start looking at relationships that they are in for a way to acquire some sense of power and control.
You will see this often in bullies.
People often think that bullies are what they are because they are simply mean.
This couldn’t be further from the truth.
In many cases, bullies are the way they are because they are trying to wrest some power from a powerless situation.
If you were to go into many of their homes and investigate their home lives, you may see children who are not treated well nor respectfully by family members.
They are not seen as particularly relevant oftentimes and may be at the receiving end of a frustrated mother, father, sibling, etc.
Hence, when said bully arrives at school and they have a size advantage over their peers, they bully and intimidate in order to feel better about themselves and regain any sense of control in their lives.
What they lack at home, they try to force into their life outside of home. Hence, bullying tactics become their staple.
Your boyfriend may be of like-mind.
He may be at a point in his life where he feels a sense of powerlessness.
Therefore, he will look to who he knows is the most vulnerable in order to gain some kind of control or power over.
You are that person.
He knows that through his words, he can have an effect on your psyche.
He can actually have influence over how you feel and think simply by joking around about your weight.
When he notices the effect it has on you, it only makes him want to do it even more because he has now tasted that sense of power that he so desperately craves.
This can be so addicting.
Hence, simply take a look at your boyfriend and what is going on in his life right now outside of your relationship.
Is everything going well?
Has he complained to you about certain aspects of his life from time to time.
Does he seem more irritable or emotionally unavailable from time to time?
If you reflect on this, there is a good chance that you will discover that your boyfriend may not be entirely happy with his life outside of your relationship.
That is a tell-tale sign that your boyfriend could easily become vulnerable to doing what he is doing right now to you.
He may not necessarily have perpetually cruel intentions in mind.
Indeed, this period may be short-lived once he starts regaining a sense of peace and control in his life.
However, this sense of powerlessness in his life in general may be his motivation.
He may keep doing this over time the more you let him get away with it.