What should i do?  

My advice is for you to stick with tennis but its up to you in the end. Bowling doesnt give you a lot of exercise because only your arm is doing the work but with tennis you exert work with both leg and arms. Even though you like bowling more why not transfer that liking to tennis and maybe when you're already a master of tennis that's the time that you can begin to play bowling again.

I think you should forget both of them and study hard so you can make a bunch of money. Unless you're trying to become Boris Becker. I always thought tennis was kind of stupid, but that's just me. Never been a fan of bowling either. And I think gold is just plain dumb.