Here are some useful expressions and vocabulary that we use in personal relationships:
to have a crush on somebody = estar colado por
Susie has a crush on her English teacher, but is too shy to tell him.
to flirt = flirtear
My brother always flirts with my friends.
to play the field = ir de flor en flor
She was tired of playing the field and felt she needed a more stable relationship.
And you can address your better half in several different ways:
dear, darling, sweetie, love, sweetheart, honey
You’ll find more vocabulary related to personal relationships in Module 9, Unit 2 in this app.