Regardless of his feelings, that property is owned and maintained by her father. It’s time to back off and stop bothering her parents.
Her boyfriend could create his own tribute to her, far away from that gravesite. He could buy a small tree or a flowering bush. Her parents don’t ever need to know about it.
This is supposed to be a conservative website. It’s amazing that many people who *think* they are conservatives don’t believe in private property rights.
Also the rights of parents trump the rights of boyfriends. Had this guy married the girl and he bought the burial plot he could plant all the flowers he wanted.