Yeah I think of it as an ethical rather than a moral issue. I don't think anyone is morally obligated disclose, but I do think that if one commits to spending one's life with someone, there's an ethical obligation for the partner to know important details about the person's life. And one of those details is their gender history. I've dated people, sometimes for long periods of time, without disclosing. But I've always told anyone I've loved.
Also, if we extend our sympathy towards transwomen who become suicidal over the issue, how can we dismiss the issues of their partners so easily?