A word for someone who never had a mate because he/she has a high standard

Is there any better word than picky?

How about romantic (or relational) perfectionist?

They developed the Multidimensional Romantic Perfectionism Questionnaire (MRPQ), to assess seven aspects of romantic perfectionism [...] (7) prescribed romantic perfectionism for one's partner (i. e., the tendency to have rigid, inflexible standards for one's own romantic partner).

^{"The Effects of Romantic Perfectionism on Disclosure in Romantic Relationships," Dustin P. Bailey William E. Snell, Jr.}

fastidious might fit in that description

http://dictionary.reference.com/browse/fastidious

You might consider "particular" as in "She's very particular about prospective mates."

From The Free Online Dictionary:

particular [pəˈtɪkjʊlə] adj ... 4. exacting or difficult to please, esp in details; fussy

If that's not strong enough, you could use over-particular.