How to Keep iPhone 3GS Jailbroken and Unlocked on iOS 4.3.3?

Hello Reema, first, I would recommend you to backup the SHSH blobs of your device using iFaith SHSH Blobs Dumper by following this tutorial so that you could downgrade it back to iOS 4.3.3 once you have accidentally restored your iPhone to iOS 4.3.5. Anyway, there is an app from Cydia Store that has capability to keep your iPhone jailbroken and unlocked, and the name of this app is called RecoveryGuard. Once downloaded and installed, RecoveryGuard jailbreak app will trick your iTunes that you have already restored your iPhone to the latest iPhone firmware as well as prohibits iTunes to put your iPhone into recovery mode.

Step 1: Open Cydia app on your jailbroken iPhone. Wait while it reloads and updates its cache.
Step 2: Tap on the Manage tab at the bottom of Cydia followed by tapping on Sources section to view your current repos.
Step 3: Tap on the Edit button on the top-right corner followed by a tap on Add button on the top-left corner. When Cydia will prompt you for the repo address, enter http://cydia.pushfix.info as Cydia/APT URL and hit Add Source button.
Step 4: Cydia will update its sources database. Once done, just simply tap on the Search tab at the bottom of Cydia and type RecoveryGuard in the search field.
Step 5: From the search results, select RecoveryGuard and tap on Install button on the top-right.
Step 6: Now wait while Cydia installs RecoveryGuard on your iPhone. Once completely installed, tap on the Reboot Device button to restart your iPhone.