How do you get someone to take care of themselves?

I’ve been with my boyfriend for almost 4 years. Things were great and we have started to build a life together. However the last year or two he’s let himself go, he doesn’t style his curly hair so it’s a mess, his greys are rampant, and he has gained at least 80-90 lbs. He’s 27 but could easily look 45 or older. I’ve often been asked if he’s my father. This has embarrassed me and now I hate being seen with him, I won’t go on dates or leave the house with him. I put great pride in my appearance and strive to look my best when I go out and it’s disheartening being with someone when people in our apartment building have even come forward to him if he’s homeless? I’ve brought up asking him to work out several times and he makes
excuses. I’ve offered to teach him to style his frizzy hair but he just gets frustrated. At this point I don’t know how to approach him about it because he just gets upset and doesn’t try to make a difference.
How do you get someone to take care of themselves?
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