I think that I am good at keeping a secrets.

I am a quiet person, so the opportunity of giving away a secret is fewer then other people.I speak to less people. There is less opportunity to share secrets this way.

I'm not that interested in gossips like cheating, because it's none of my business.

I might seem to be a boring person.

Are yYou gGood at kKeeping a sSecret?

I think I a'm good at keeping a secret.

I a'm a quiet person, so theI have fewer opportunity ofies to givinge away a secret is fewer thean other people.

Changed the word order to make it more natural.

"Then" is used for marking events. "Than" is used for comparisons. For example: "I went to the grocery store and THEN I went home" vs "I am taller THAN my sister"

I'm not that interested in gossips like about cheating, because it's none of my business.

I might seem to blike a boring person.

Or you could say "I might sound boring", which might flow better.