22-year-old Hazuki lives a boring life in an apartment filled with plants, but secretly he couldn't care less about the vegetation, for the highlight of the young man's day is buying the items from cheery Rokka, a widow who runs the flower shop nearby. So that he can spend more time with her, Hazuki eagerly accepts a job working part-time at the shop, but after months of working with his crush, the man can't seem to muster the courage to confess his feelings. And it's not just his abrasive personality getting in the way of his ideal relationship - the ghost of Rokka's dead husband haunts the shop and is determined to keep all potential suitors away from his wife. Despite this unexpected obstacle, Hazuki continues his attempt to woo the older woman and free her from the ghost of her past.
Natsuyuki Rendezvous and the first story from All My Darling Daughters are both about women and their younger male suitors. Both manga have a similar emotional yet low-key tone, and feature untraditional romances that have their share of hardships/quirks.
Though Natsuyuki Rendezvous is a supernatural josei romance, and Breathe Deeply is a seinen medical drama, both are mature manga that prominently feature love triangles in which one of the characters is already dead. It's a pretty rare twist on the theme, so if you enjoyed that facet in one, you may like it in the other.