Final answer:
Erich Fromm suggested that falling in love is different from being in love in terms of facing living realities. Sigmund Freud's ideas, especially about sexuality, influenced the new morality of the 1920s and liberalized societal attitudes.
Step-by-step explanation:
The psychologist who suggested that falling in love is very different from being in love, which involves facing the realities of living together, is Erich Fromm. This question seems to be connected to the broader context of psychology's influence on culture and social practices.
The popularization of Sigmund Freud's ideas, particularly his theories on the unconscious mind and sexuality, encouraged the new morality of the 1920s. Freud's work challenged traditional Victorian values and promoted a more open conversation about human sexuality, which in turn influenced the cultural shift toward more liberal attitudes in that era.