The 5 years you are talking about, sure Kunal wasted but where they by choice?It wasn't only Richa who rejected him, but his family and society as well. Characters in the show also made same mistake. Raj had stopped talking to him, Thakral made sure no one gives him job and he was thrown in back. So drinking, gambling and self-destructive nature wasn't simply because of Richa, but everything together. Whatever he did for Richa was in good faith. He believed Richa is good friend so he tried to help her, nothing more. even when they claimed "love" it was more of college time relationship and not serious at all.When Siddhi left, he had his entire family, son and opportunity, yet he broke down. He was afraid to walk-into court, couldn't look in mirror, didn't celebrate his B'day' all because Siddhi wasn't there. Siddhi who was believed to have wronged him big time. You are right about both having similar character of honesty, helping nature, akdoo/ziddi, etc. So no one can come close to Siddhi.