One thing we know about Romeo is that he is a sincere person. We see his quality of sincerity in the very first scene. First, we learn from his father that Romeo is feeling genuinely, deeply, sincerely grieved over some matter. We know of his sincerity because he has been seen staying out all night and also seen crying each morning at dawn while standing in a certain part of town, under a certain grove of trees. Most likely, he stands all night long in the same part of town where Rosaline lives, and the grove of trees offers a view of her house, possibly his bedroom. His tears show us just how deeply and sincerely he has let Rosaline's rejection affect him. Romeo's emotional state is appearing to be so sincerely troubled that Lord Montague is afraid Romeo will do himself some harm if he keeps rejecting counsel, as we see in Lord Montague's lines addressed to Benvolio, "Black and portentous must this humour prove / Unless good counsel may the cause remove" (I.i.137-38).
Romeo's sincerity also shows when he first enters the scene and is sincerely troubled, even frustrated and angered by the signs that there had been another fight. He even rightly points out that the feud has just as much to do with the two families' own love for themselves and their own ideals as it has to do with the hatred each family feels for the other, as we see in his lines:
O me! What fray was here?
Yet tell me not, for I have heard it all.
Here's much to do with hate, but more with love. (171-73)
Another one of his qualities is that he is generally virtuous, even pious. Even Lord Capulet speaks of Romeo's reputation for being virtuous when he commands Tybalt not to fight Romeo at the ball, saying, "Verona brags of him / To be a virtuous and well-govern'd youth" (I.v.70-71). We especially see Romeo's virtuous and pious mind when we see him feeling such deep regret and remorse in the final scene over killing both Tybalt and Paris. He shows feelings of regret over killing Paris when he says to his corpse, "O, give me thy hand ... I'll bury thee in a triumphant grave" (V.iii.81-83). Shaking hands is a sign of forgiveness and mutual respect. Therefore, by asking the dead Paris for his hand, he is asking him for his forgiveness. He even asks the dead Tybalt for his forgiveness, again showing us Romeo's virtuous and pious mind.
"Verona brags of him / To be a virtuous and well governed youth"(1.5). He is also a "young waverer"(2.2) and "renown'd for faith"(3.2). Though he does kill himself with poison, as Samuel Johnson suggested and Isaac Asimov noted, the matter of the so called sleeping potion is altogether fictional, that is, recovery from the effects described by the Friar is impossible. So one might pardon the offense.