Impulsiveness is acting quickly, particularly in decision-making. If you are looking for another tragic flaw of Romeo, you may consider long-suffering.
When deemed banished, Romeo spent forever crying and pouting and rolling around like a baby in the Friar's cell. When the play opened up, we were told about how he would spend tons of time on his own out by the sycamore grove or in his room just being depressed. Finally, by the end he is banished and has to spend seemingly endless amounts of time in Mantua. Although this idea is connected to emotions, and a result of sometimes impulsive decisions, it is not the same as either. You might also consider the fact that his suffering often comes from the feud between the families. See if that works for you and read through the link below about tragic heroes and maybe a different connection would surface to you.