Yes, unfortunately, you will have to tell him at the end of the day, he is your father. Keeping this hidden isn’t a long-term solution anyway; how long can a situation like this really sit in the shadows? Indian family dynamics can bring a lot of drama and friction, so your hesitation is completely valid and understandable.
However, your plan to disclose it by the end of the year shows you are on the right track. For the practical side of how to approach the conversation smoothly, look up tips or videos online people who specialize in family dynamics often have great communication tactics for opening up about secret relationships.
Whatever happens, don’t panic. Take the step with respect, keep your composure, and trust that we don’t land in any situation by random chance it is all part of a larger divine trajectory. I hope your father and the family come around will pray for you the best.