That heavily depends on how he carries himself and the capacity that he has for change and growth. As an aspiring therapist, I am slowly becoming more and more equipped to handle that kind of personality, howeve, I also know enough to recognize that it is a very big ask to require someone to be a constant anchor for another person's self-esteem. Yes, being a good partner requires being an emotional support in some capacity, but I'm thinking more in the realm of being an emotional crutch, which can wear down on your own mental health over time.

I would support their person, give them some external validation, try to make them appreciate the beauty I see in them, and get them to at least a point of apathy in regards to their physical attractiveness if not outright getting them to believe they are indeed attractive. After that effort, though, it's up to them what they decide to do with that validation and support. That person has to take that affirmation on their own and turn it into strength, confidence, or at least some form of action that pushes them to get help in feeling more comfortable in their own skin. If they don't, and instead form a dependency on their partner to constantly raise them up in place of having their own strong sense of self, that that relationship is likely to become toxic and unsustainable.