Here are some titles that i loved as much as Here U Are x3 with kinda similar vibe, a sweet and fluffy story. Tho as mentioned before me, we could help better if you were a little more specific about what you liked about it :3 (note that some are yaoi and not shounen ai)
For Your Love
The Man Who Can't Taste
Love So Pure
Serious Joke
Minority
Intoxicated
After Staring at the Starry Sky
Light-hearted with solid relationship building. I love a smutty yaoi as much as the next person but I really enjoyed how realistic the interactions were and the growth of characters.
I've also read/reading Sign, Semantic Error, our sunny days, nerd project and my guildmate next door. Those id say are the closest I've found. Any other recs?
I've been chasing the high I got reading Here U Are but nothing has scratched the itch. Any recommendations?