"By the way, she has a boyfriend."
Translation:Parenteze, ŝi havas koramikon.
I don't think the meaning the same, because there are two distinct use cases.
Parenteze is "let me say something that's not part of my main point but I want to mention in passing. I'll come back to my main point right after". Cetere is "I've said things, and in addition I'm going to say other related things"