Here are two instances in a formal paper I submitted where my professor told me my semicolon usage is incorrect. (For the record, he told me this as he was reading it for the first time. He said most students use semicolons incorrectly and to avoid them altogether. I'm not .)

Here are two instances in a formal paper I submitted where my professor told me my semicolon usage is incorrect. He says that, in both instances, a period should be used. Is he right? I maintain that I've used them appropriately and at my discretion to indicate closeness of subject matter between two independent clauses.

Instance 1:

Baz Luhrmann, in his 2013 film adaptation of Fitzgerald’s work by the same name, represents its major characters in a manner mostly true to the novel; Nick, Gatsby, Daisy and Tom are somewhat polarized, however, in their speech and actions.

Instance 2:

In the novel, when Nick is “urged” (28) by Myrtle to go along, bribed with the promise of Myrtle’s sister, he responds “Well, I’d like to, but—” (28); in the film, he worriedly says, “No, no, no—that’s alright.”