do you think jackie was right to break up with hyde when he said "i dont know" to them getting married someday?
I think Jackie's question is the wrong one and that Hyde's response is too simplistic for his character. (IRL, the showrunners and writers were working toward series finale where Hyde proposed to Jackie, and that exchange is part of leading up to the finale).
Let's go with Jackie's in-show question for now. Hyde is too thoughtful and too in love with Jackie to say merely, "I don't know," or shrug. He also has an excellent memory about what's important to him, and he would remember the events of "Do You Think It's Alright?" (6x18).
Hyde would say, "Why are you in such a rush, man? You're goin' to college soon. I'm still dealing with the fact I got a family I never knew I had and a tryin' out this record-store thing. We got plenty of time."
Jackie: But what if we don't? If we get married then I'll know we'll be together forever, and I can finally stop worrying about it.
Hyde: Forman and Donna got engaged, set a date for their wedding, and Forman ran out in her -- and Donna almost ran out in him. Bud and Edna got hitched, and Bud ran out on her. Your folks are still married, but your ma hasn't acted like it since before your dad got arrested for bribery. So marriage isn't the guarantee you think it is.
Hyde: No other chick I see a future with besides you. No one else I want a future with, and I'm not gonna screw that up by getting hitched before the time is right.
Jackie: Are you saying we're engaged?
Hyde lightly punches the center of his chest. "Where it counts, but nothin' official, so don't --"
Jackie: Oh, my God, we're engaged!
She hugs Hyde tightly, and Hyde chokes out, "Engaged to be engaged."
Jackie: That's good enough for me!"
Jackie's question shouldn't have been about marriage but about Hyde's commitment to their relationship and their future. When he imagines his future, what his family looks like, are they still in love?
Hyde doesn't like to think about his future. He's not that guy. He lives day by day. If life's taught him anything, he can't predict crap. He just rolls with the punches.
Jackie: Then what does that mean for us?
Hyde: Alls I can tell you is any future I got will suck if you're not in it.
Jackie (translating Hyde-speak): Because you love me.
Hyde: I love Led Zeppelin. I ... look, I have thought about my future a couple of times. I lost you once 'cause I was an impulsive, pissed-off dillhole. Not gonna be impulsive, but I'm also not gonna leave you danglin' like a worm in a fish hook. I want my future to be our future, okay? I hope that's enough for you because it's all I got right now.
It is, and Jackie's anxieties fade.
But the above is character-driven, character-first storytelling. Organic. T7S had plot ideas, a series finale they were working toward, so they manufactured conflict and put words in the characters mouths to serve plot and that series finale (which was rewritten into a cliffhanger once S8 was greenlit).