Grief is a synonym of Suffering. Suffering is the opposite of Happiness. Living can cause/lead to Happiness. Living can be used for Existing. 
Bitter is a type of Taste. Taste is related to Lemon. Lemon is a type of Plant. Plant is related to Rubber. 
Grief <--Synonym--> Suffering <--Antonym--> Happiness <--Causes-- Living --UsedFor--> Existing 
Bitter --IsA--> Taste <--RelatedTo--> Lemon --IsA--> Plant <--RelatedTo--> Rubber 