BitLocker issue. Recovery Key is required on each startup after installing secondary OS

You need to log into Windows 7, suspend Bitlocker (no need to disable your TPM), then reboot your computer into Windows 7 again (and reenable Bitlocker if it doesn't automatically do it). This will "reset" Bitlocker to understand your new dual-boot configuration. Once you've done this, you should not need to enter your recovery key the next time you boot into Windows 7.