The nurse and Friar Lawrence have different attitudes towards love. As comic relief, the nurse focuses more on the sexual aspect of love: she prefers Paris to Romeo because she says that Paris is better looking. She also makes crude remarks about both of Juliet's wedding nights. Friar Lawrence focuses much more on the spiritual aspect of love. When he marries Romeo and Juliet, he tells them "Love moderately; long love doth so; Too swift arrives as tardy as too slow." His advice for a happy couple is about how to love each other everyday, not just in bed, like the nurse's advice.
In addition to the above answer, the Friar also perceives the love/marriage between Romeo and Juliet as a possible remedy for the feud between the two families. The Friar hopes that through the marriage of Capulet and Montague children, the two families will begin to get along with one another and stop their violence and fighting in Verona. The Friar states, "...this alliance may so happy prove; To turn your households' rancor to pure love." (II. iv 91-92)