The Goodbye Girl (1977) on Netflix

Ex-Broadway chorus dancer Paula McFadden lives with her eight year old precocious daughter, Lucy, and Paula's lover, actor Tony De Forrest. Paula has solely been playing "wife" and mother ever since she got married to Lucy's father. Paula comes home one day to find that Tony has left her. Not only will Paula have to start working again (as Tony was the household breadwinner), the only thing she knows being dancing, but she may have to look for another apartment. Unknown to Paula, Tony, whose name was on the apartment lease, has sublet it to Elliot Garfield, an actor from out of town who has come to New York to appear as the lead in an off off Broadway production of Richard III. Paula will not give up the apartment without a fight - she figures possession is nine tenths of the law - but an equally tenacious Elliot figures the law is on his side and he does have a key. So pragmatic Paula figures the easiest thing to do is to share the apartment with Elliot. Paula doesn't much like Elliot, solely because of what he represents to her, and thus Paula tries to make his life as miserable as she can there in hopes that he will leave. However Elliot and Lucy get along famously. As Paula and Elliot try to co-habitate, they each have their own professional problems, Paula's being that she is woefully out of shape to be a dancer, and Elliot's being that he doesn't see eye to eye with his Richard III director, who wants to take the production in a whole different and unconventional direction. As each tries to earn a living, they find that they are falling for each other. But Paula, a two time loser in love, is hesitant to get into a relationship with Elliot, who she sees will ultimately leave her like all the others have before.