What figure of speech is " Jesu Maria, what deal of brine / Hath wash'd thy sallow cheeks for Rosaline" and what does it mean

This is Friar Lawrence speaking to Romeo. The line could be rephrased as

How many tears did you shed for the love of Rosaline and how many tears did it take to do that.

Romeo was really one love sick puppy over Rosaline and now he's even more gone on Juliet. Father Lawrence is just in awe of that transformation. Washed is a personification. You should go to this speech and read the rest of it.

Friar Lawrence is really giving Romeo a dressing down and in so doing, he is making a comment about the nature of men in general whose fidelity he thinks little of. It's a wonderful speech. Makes us humble to be called down that way.