It is really hard for someone who has a personality disorder from the cluster of disorders I suspect he has to think that seeing a psychologist might be necessary. This is because he actually does not care at all how he treats you, how you feel, or what effect his words have on you. In other words, as far as he is concerned (as illustrated in his response "What about my dream for a a second child?") it is 100% about him, what he wants, whether he is going to get it, and what you want or need doesn't figure into it at all. From his pov the only person here with a problem is you.
He sees what you have done in gaining weight as an insult to him. When you were slimmer you reflected back to him the image he has in his head of the sort of woman-shape he thinks a man of his importance deserves. Now that you look more commonplace/less supermodel (in his eyes) you no longer serve as an ego boost to him. Instead you remind him that he is an ordinary man, living an ordinary life. This is unforgivable because in his head he is not one bit ordinary. This is what he meant when he used that phrase "I've never forgiven you for becoming fat."
He does not see you as a three dimensional, fully functioning individual separate from him -- you are an extension of his own personality.
Please disabuse yourself of any notion that you are going to play the role of ministering angel to a troubled soul here, or wise facilitator who steers a sad and tortured man in the direction of some magical, effective cure, that he will be grateful for managing to restore his happiness, and that a harmonious life and second child together, picket fence, nuclear family, etc., are in the future if only you try hard enough to make him see...