Breaking a vow

Q: I had made a vow that if I do a particular sin ever again in my life I will pray so many number of Rakaats. However I am finding it difficult to fulfill the vow because I keep relapsing into the sin. May Allah help me abstain.Am I allowed to change or break the vow so I no longer have to pray those many numberof rakaats?

Forgiving someone

Q: How do I know if I have forgiven someone? I had slept forgiving someone but after waking up, I again felt bad about that person, though I didn't have any bad feeling or hatred that night.

Taqleed

Q: Charo Imam saheeh hai to kya charo ko mila kar follow karna kaisa hai? Kya maslak ko badla ja skta hai ek se jyada bar?