is it ever addressed that she got together with him because of one of her exes? not yet (chapter 34). I'm not sure it will ever be adressed, but it's a posibility. I personally think that depends on if you believe "sensei" (meguro's first love) will come back or not. I think it will come back (maybe not physically) because, even though meguro has now chosen Koga for herself (chapter 30 would be the point), that stills needs to be settled out loud... and it also could be an interesting drama plot.
is it ever addressed that she doesn't really like him, that she only likes what he represents? I think it's like that for a lot of series and also real life. There is always a mix of the person and what it represents in your own life, but Meguro does in fact fall in love with the MC. If I had to pinpoint the moment it would be around... chapters 23-24 when that arc started and really develops around chapters 29-31 with the school trip. There is a great progress in Meguro when it comes to healing from her past viewpoint and changing her ways (which is why i consider this manga a character study for Meguro, but i'll talk more about that later). That really starts to show at chapter 32, with the part time job thing.
is it ever addressed that she doesn't know anything about her BF, I bet if you were to ask her what his favorite color is, she wouldn't know? I think this manga is a character study and the subject of the study is Meguro, so the story actually revolves around her, that's why whe know so much more about her, even if most of the time we see what Koga thinks. Even though we see koga grow, the actual conflic of the story is Meguro dealing with her past (particulary "sensei" and her own self-confidence) and what it means to have a relationship, be in love and choose for herself. But there is a point where this is somewhat adress at chapter 25, when the MC prepares for his exams (which is the only thing this character ever does when he is not around his girlfriend... that also is a preview of the answer for the nex question).
does the dude at some point get more development that doesn't involve the gf? does this dude have any hobbies? what does he do in his spare time? that would be just adding a trait. It has to come when it's compeling for the characters. A story is about character growth. Giving a character a hobby of other activies is just facts. Even if you think that makes a complex character, complexity doesn't make a character compelling either. Character growth usually comes from interaction (with a friend, a mentor, a romantic interst, the villain, etc). If the hobby or extra activity doesn't have a porpuse for the relationships then it might as well not be there... and that goes back to my point of this being a character study for meguro. She actually does get a part time job, while koga just focuses on his studies. Koga focusing on his studies made it harder for them to meet. That free time (and the fact that meguro's friend had a part time job) drove meguro to get one. That also comes around when the "sensei" arc comes to a close and the "self-confidence" arc begins. I think that is a good use of hobbies/spare time. One of the only props I can give to the author.
the fuck is wrong with this people? I ask myself the same thing in the real world but if you need an answer I think the problem it that the characters are made around their flaws and not the other way around (making a character and giving them a flaw they have to overcome). There is no character outside the "simp" for the MC because that was his defining characteristic. The same way with the "kuudere slut" for the FMC. This exacerbate their flaws which can make it hard to watch for some people. You could say the story is about them trying to scape those tags. I don't think that's what the author is doing, but that's the way i'm reading it... on the other hand the author has a real issue with pacing, some things happen too fast and with little explanaition as to why characters (particulary secondary ones) do the things they do. I see this as a flaw in the author and not in the story. I have a weird look at it i know.