I began my anime watching "career" with the usual romcoms too, and I loved them! Granted, I was in highschool or just out of at that time, so I could still relate. Over time though, it seems like 90% of romances are only in high school. I'm probably in my 6th year of anime now. So it's not that high school romances are worse quality-wise or anything, but it's that I've seen a lot of it, so I'm always alert for something new, especially if it takes place after high school.
But yeah, some high school romances (not all) are just about one specific school year. Sure two people may get together at the end of the anime, but they have 2 more years of high school to go and the rest of their life, so who really knows what's going to happen? But the anime usually implies that it's the "one true love" for both characters, which is where I sort of have a problem.
Spoiler for Kimi ga Nozomu Eien:
You said above that you wish he chose the other girl, but maybe I like it because it's not the typical "everyone lives happily ever after" ending. When I finished watching the anime, yes, I also wished that he would choose the other girl! Because that would be the ideal couple, wouldn't you agree? After that though, whenever I think about it, I begin to appreciate the tragic situation that the characters were put in, what Takayumi went through during SH's coma, and his relationship with HM. Lots of people think HM is a bitch for doing what she did to her friend, but love isn't ideal. Sometimes, it comes at our worst moments, and I think it's exactly the frankness of the situation that made me like the anime so so much.
It's also why CLANNAD (both seasons) is my favorite anime right now. I'm not too keen about who won (Tomoyo is my favorite character), but about how the relationship developped. Season 1 was comedy-filled and serves as a great introduction to all the characters. Then Season 2 was what I've been waiting for, and I really appreciate how much Key tried "finish" the relationship.
So all of that comes to my recommendation for this post, which is
Nodame Cantabile. The setting is a music college, and the main protagonist already has an ex-girlfriend, so there's none of that "first love, true love" situation. The romance isn't dramatic and serious and it's interspersed with a nice balance of (classical) music and comedy. What I love was that it focused on the main characters' development while having a plot. The "feel good/coming of age" element from slice of life combines very nicely with the romance. This may not be your thing, but if you're looking for having a good time in general, then try the first season.
When I was following Nodame Cantabile, every episode makes me feel happy that day, no matter if my week has been shitty.