@HammerU89
Different situation entirely. For starters, Shizuku and Haru essentially split up and didn't get back together until after college, so whether they were still informally set on each other or not neither had to put their life on hold while the other left to pursue their aspirations, rather they opted to do so separately and picked up where they left off years later.
Secondly, in doing so they reconnected on equal terms both having achieved their respective goals and making a point of balancing their aspirations and their relationship, something that had been one of the overarching themes of the story forcing them to grow as people and make hard decisions about their relationship and respective futures. There was even a scene with Shizuku's workaholic mother, like the one with Kiyoshirou's mother from this chapter, where she tells her the opposite of what Kiyoshirou's mother said, that if she wants both she has to work twice as hard for it.
@FredFriendly
Of course, I am sure there have been but at least in my experience with these stories, it usually isn't scenarios where one side completely leaves the country like this. Normally, we're basically talking about different schools in the same or other prefectures which isn't that much easier but it's a fundamental issue of accessibility. Someone could conceivably take a multi-hour train ride to another prefecture or even relocate, but it's significantly harder when you're talking about a plane ride to another country. Not to mention that short of Japan's more prestigious universities if it's just about going to college elsewhere it's a lot less difficult to keep up or follow them even if you aren't pursuing the same subjects, but going abroad is a different story.
Further, you also have to consider their respective outcomes. In most cases, you're talking about going away to college and coming back to a normal career, but Kiyoshirou and his mother have both basically told Koharu in no uncertain terms that his career takes precedence over her and if he's anything like his mother, it will always be that way (and we have good reason to think this, back when he went to visit his grandfather he was so wrapped up in the work that he didn't even bother to call her and even when he realized it, he still chose not to bother). It's one thing if you're going away to return to a normal career but it's very much another if nothing will change and you working becomes indistinguishable from when you were away.
She certainly seems to me to be one of those women that "can handle it."
If you think she can handle it, I don't think we're reading the same book. When Kiyoshirou bugged out last minute to visit his grandfather she was on the verge of breaking down almost immediately the moment she didn't see him in class and even though she had only just met Edogawa for the very first time that day after dropping by Kiyoshirou's house, her unhealthy co-dependence immediately shifted over to him and she spent the entire time Kiyoshirou was away clinging to Edogawa and was still barely hanging on for dear life.
And ever since Kiyoshirou left that first time and she started to get an inkling of what both him and his family were like, she's been desperately trying to convince herself that she'll be 'okay' when he goes. And it only got worse after he told her of his plans (not to mention how she nearly had a breakdown just before that thinking that he was going to break up with her.) At this point, Koharu largely only exists as an extension of her infatuation with Kiyoshirou. It's right there in her monologue and thought process, she's no longer even thinking about her wants and needs just how it will be okay when he's gone because she can't think of anything else but him. That is the furthest thing from a healthy attitude. She's losing herself in her affection for him and doesn't realize how irrational her thought process has become.