Hello basl it sounds like not necessarily a weight issue to me, more of a confidence issue. It sounds as though your confidence is terribly low and you are in a cycle of no confidence so daren't try: haven't tried so aren't confident, and so on. When he says "snap out of it" he can't realise how hard that is.
Basl weight is an easy thing for someone else to focus on. I wouldn't be mad or sad about the comments, it's so unproductive. You should focus on something else for a little bit. OK I am going to sound like an advert here but.. you are worth paying attention to. You are worth a bit of tlc, a hairdo, whatever -- not for anybody else, but to put a smile on your face, make you feel refreshed, to face the day with an extra bit of confidence. If you do these things for someone else, you aren't out of that cycle: you are looking for approval and waiting for failure if the approval doesn't come.
Giving yourself confidence in tiny steps is like compound interest on a bank account: things accelerate more quickly than you expect.
For a start, if you can afford it, have your hair done. It's a tiny, apparently shallow thing, but can make a huge difference to confidence, can get you compliments, which make you smile, which make you feel brighter.. all of which you take home and feel stronger with. It is like a rolling snowball. But if you are making changes, do it for yourself, and not for approval.
Good luck