Ookami wo Karu Housoku
Sayonara Alpha
This is really good. Specially cause the omega waited for his alpha to grow up.
Shinkuu Yuusetsu
This one's a very interesting read. It's about a country where everyone is matched with a lifetime partner when they're 3-4 years old. However, being partners is different from being married as you can have both a lover and a partner (but your partner is always your most important person). Furthermore, no one places priority on love and romance, so even if two partners have have sex or develop a family, their relationship is still more platonic than anything since it comes from the mutual understanding and acceptance that they will always be together until they die.
Koi wa Ina Mono Myouna Mono