The concept of the Petrarchan Lover comes from Petrarch and his sonnets. Petrachian sonnets have a specific structure and form, different from Shakespearean sonnets. Petrarchian sonnets are structured into two parts: an octave (or eight line block of verse) with an abbaabba rhyme scheme, and then a sestet (or six line block of verse) with a few possible variations on rhyme scheme.
Petrarch wrote a series of sonnets to an idealised lady named Laura, with whom he had never even had any conversations. He was responsible for creating certain ideas about love and relationships, bringing in the concept of falling in love at first sight and needing to know nothing about the object of your affection to fall in love. Although Petrarch lived between 1304 and 1374, his sonnets were immensely popular even in Shakespeare's day. One key notion that is important to these sonnets is that the lover's affection is not returned and as a result he suffers a flu or cold because of his love-anguished heart. Interestingly, we can see an example of this in Shakespeare's Romeo and Juliet. Romeo describes his love for Rosaline in this way, as he says he is "sick" and "sad". Shakespeare of course deliberately set up Romeo as a Petrarchan lover in this way to highlight his love for Rosaline with his love for Juliet.