ok, i will try to answer u one by one:
2) who is this Garv, Kali and Kumud?- do u remember Mahi, the lady Kkusum brought home for a baby? Kali is Abhay and Mahi's daughter. Kkumud is Kkusum and Abhay's daughter. Though she looks older than Kali, she is a couple of months younger than her. Garv is Khithiz's( Aryman and Shaakshi's son) friend. First, he got engaged with Kali. Then got married with Kumud. within a month he was back to Kali, sleeping together. Kumud got to know that and divorced him. Now he's married to Kali.
1) After a leap, how did abhay and Kksum reunited?- After the leap, Kumud and her friend came to Mumbai to study. She also worked with some party organizers and arranged Kali's Birthday party. She became almost a family member. After some months, Kkusum and Ayi came to mumbai. Abhay saw them, but thought it's just a illusion. Mahi saw her and requested to come back to the family. However, Kkusum denied and Mahi got married with Abhay. Kumud was told by Nakul (Aryman and shaakshi's younger son) and his friend Harry. She hated Abhay. Then one day, Kkusum got to know the truth that abhay was never a traitor. She forgave Abhay and 3 of them eventually re-united.
I hope i answered u right. It's a long story and hard to remember the whole thing. So, if u want to know everything accurately u have to rent lots of videos and watch them. So better take some time off from ur job/study and stay home to watch the whole thing. U need more than a month😊