3D Kanojo - It's a rough show (quality wise) but has a really solid ending.

Tsuki ga Kirei

Toradora - Have to watch the after credits.

Ore Monogatari - The whole thing is a happy ending.

Wotaku - Same as above.

Tonikaku Kawaii - Same as above... for now.

Kimi ni Todoke - The second season gets a little frustrating, but both seasons have good endings. S1 ends on a fantastic New Years arc that is perfect for this time of year.

Fruits Basket (2019) - The 2001 adaptation is not a full adaptation, but the 2019 remake is. 3 amazing seasons and a Prequel movie.

Lovely Complex

Ristorante Paradiso - Not a complete adaptation, but show leaves things off in a good spot without needing you to continue.

Yamada-kun and the Seven Witches - Same as above.

The Pet Girl of Sakurasou - Same as above. Source material after what the anime adapted was not well received.

Inu x Boku SS - Source material after what the show adapts takes a shift into more serious material.

Golden Time - Ending is a mess, but it's a happy ending.

Love, Chunibiyo & Other Delusions - 2 seasons and a movie. Doesn't feel like everything is truly resolved by the end, but it's a happy ending.

Quintessential Quintuplets - 2 seasons and a movie. You'll probably half to wait for CR to stream the movie. It was only in theaters for a week over here in the states.

ReLIFE - Final arc is a little rough in terms of quality, but it's still worth watching.

Saekano - 2 seasons and a movie. S1 is on CR. S2 isn't anywhere anymore. The movie was never made legally available to stream.

Tada Never Falls in Love - Hint, he falls in love... in like the first 5 minutes.

ef: A Tale of Memories - Multiple romance plots intertwined.

Orange

Oresuki - The movie's ending doesn't seem to be fully committed but there's a line at the end that suggests otherwise. You may have to Google it after the fact.

Science Fell in Love, So I Tried to Prove It - Just the first season. Second season does not really stick the landing and goes in a direction many did not want to see the story go. Just watch S1 and be happy with how it ends.

Waiting in the Summer