The sentence doesn't read very natural to me. I'll critique it to give you some ideas. - "... DIDN'T FEEL sad despite PARTING ..., because they RETURNED ..." is unnatural. Make it DIDN'T FEEL ... because they WERE RETURNING ..., to mean how they were feeling about going home. - "despite" seems to be unnecessary. I think it sounds better without it. - "parting with" a place doesn't sound natural. You part with a thing or person, not a place. - "this place" might not be a good choice as it can sometimes sound derogatory. Better to be more specific. - "fully loaded" doesn't sound like a good choice in this context. I would write something like these: - They didn't feel sad to leave the school, because they were returning home more knowledgeable and accomplished. - They had no regrets heading home, as it had been a time well spent with a lot gained. - They felt good when it came time to go home, because they believed they had completed a productive N years of their lives. (substitute actual number for N)

I'm a bit confused. You say "I'm trying to say", but you don't know what the phrase means? I think it's grammatically correct, but it's not quite natural. "parting with something" usually means giving a thing away, or losing something. I think it's a little odd to use to mean "leaving". "return fully loaded" is usually tangible. It is used to refer to a truck or ship or something similar that is full to capacity, when it returns to its "home". I can't see how a person's brain can be fully loaded, so to me it feels a little odd in this context.