Is manga necessary to enjoy the anime as I have never read a manga in my life and until now for 2 years, I am watching anime only.
If you've been watching anime-only for years now, I suggest that you look at the manga.
In the title, you refer to the anime XYZ as famous, and as most anime are adaptations of the manga, if they have reached fame, the manga version is most likely going to be just as good. For someone who has been looking at Japanese art for years now, yet only anime-only, I suggest that you read the manga, simply to try out new things. This answer is purely on my experience with Japanese publishing (e.g. manga or anime), and all the good anime I watch have manga just as good. So I'd suggest if you've been watching a famous anime, you check out the manga version as well.
This is just based off my experience, but if you wanna ask me, you should read the manga of anime XYZ as well.