So, this -LEK ending refers only to 2nd person SINGULAR? If I'd like to say 'I love YOU GUYS', that wouldn't be correct and i'd have to add 'titeket'?
The object of the "I->you" form -lak/-lek may be either singular or plural. This sentence could mean "I love you guys." If you feel that the meaning is not clear enough from context, you can include the object: szeretlek téged for singular "you" and szeretlek titeket for plural.
Once I learned, that for the case of "I => singular you" = "Én => téged" can be expressed just by the verb with the suffix -lak / -lek.
Thats why: Szeretlek. => I love you.
For the case of "I => plural you" = "Én => titeket" you are not allowed to leave the accusative pronoun.
So: Szeretlek titeket. => I love you (guys).
No special ending. Just Mi szeretünk téged. But the mi is optional and the téged is even optional if it can be understood from context, so it could be as simple as just the verb:
-- Szerettek engem?