Just guessing:
Barefoot in the Park
(for some reason I see Robert Redford)
or Albert Finney
Two for the Road
Tom Jones
Not Barefoot in the Park, or any Robert Redford movie. Mr. Redford is undeniably a fine-looking man, but I think the first movie I saw him in was Butch Cassidy and the Sundance Kid, and the movie I have in mind is just a little bit earlier than that (so I had already formed my crush on this other actor before I ever laid eyes on Redford).
Oops, we crossed! Yes, it's Two for the Road (a very funny scene). And it was Tom Jones where I first fell for Albert Finney.
See my post above yours (we've got to stop crossing like this!)
I haven't seen Two for the Road in a long time, but something told me to try it. And yes, I have been spending toooo much time on A2K. (lol)
Oldie (No tie-in that I'm aware of)
The uneducated young man with no social standing hitches a ride to the city. On the way a beautiful girl whizzes by in a fancy red convertible, a girl he will fall madly in love with. In the city, his uncle finds him a job in the family bathing-suit factory.
OH! One of my favorites. A Place in the Sun.
(raggedy, we're repeating ourselves!)
Oooh did we ask this one before? Yes, the pool table scene was yours, wasn't it, EOE? A Place in the Sun is one of my favorites, too.
In-betweener
When he offered to take her arm to assist her, she insisted that she could manage on her own just before slipping and rolling all the way down the stairs.
Barefoot in the Park (Fonda's mother)?
Yep. It was an easy one. You'd just mentioned it above. Mildred Natwick played Corey's mother. She was hysterical, wasn't she?
I loved it when she climbed the stairs huffing and puffing to their apartment for the first time. She said she thought she'd died and gone to heaven. I liked Charles Boyer, too. (But I always like him. )
Newbie:
He sits alone some distance from the businessman's birthday party, and as he views the magnificent fireworks display he's filled with emotion. We see a teardrop fall.
Yes indeed. Meet Joe Black is correct.
I must log off now. Have fun.
In betweener:
When her trick went over to comfort the crying child, the prostitute mistook his attention to her daughter and began to pound him with her fists.
Darn. It's very familiar. Here are three for a clue:
Last Exit to Brooklyn
Pretty Baby
Cinderella Liberty
None of the above.
new clue: she lay her head on her mothers' knee until, visibly uncomfortable, the older woman moanfully urged her daughter to move away.
bonus-we've done this one before also.

I know. I know. But, I've forgotten it. Now, I'm thinking - Marnie.