It's very slow/non existent development, and everything sort of just - happens! The characters are also more 2D because of that. For people who prefer more realistic developments and would prefer a faster pace, this isn't the manga for you. Yet, there's something rather dreamy about how the manga plays out, and I'm sure the pretty art helps with that - the pacing almost reminds me of Taiyou no Ie, but it's...better. It's gentle. The slow but also somewhat random developments between characters and relationships is old school, and that's not a bad thing - it resembles the romantic daydreams of a stereotypical school girl, you know? Or another way to describe it - those old dating sims where target-MC interaction is low, but the romance blossoms just by seeing each other however briefly. It's not realistic at all - but once in a while, something as silly as this sort of romance is cute.
To be more critical, the way the characters treat each other can be problematic and unhealthy, although it's not quite a surprise (not an excuse, but Japan has a much different culture and therefore much different takes on gender roles/relationships/etc - unfortunate, but true). In more recent chapters, it seems that they're take steps to know exactly what their relationship is like and how they will work it out, I'm a little happy. The girl seems to remain as dependent as ever! Sometimes, that's not quite a bad thing, and it makes sense considering she's extremely shy/possibly insecure (I, uh, relate, unfortunately, to both), but through both feminist and literary lens? Hopefully she'll become more independent & decisive (and there are few signs here and there that she is), because that would make a truly great story. (But, as said before, the plot is just shallow, but with romantic daydream quality.)