Flying to his house... Can I return my boyfriend's passport to him

Flying to his house... Can I return my boyfriend's passport to him?
Please forgive me for this question, I have anxiety issues... Quick Fact: I am Canadian, my boyfriend is American, we have a lot of traveling to do each year! So it was a 2.5 hour flight to get my boyfriend to the Buffalo airport so he could fly home (cheaper than an international flight). No problem. I approached the border, reached for my Canadian passport... And there's his US passport sitting along with it. Huge "OMG" moment. Called him up, he got cleared with his driver's license; thank goodness for domestic flights! Tried to UPS his passport to him... They won't insure the document, and they make it VERY inconvenient for him to go and pick it up. Seriously, I don't trust any service that won't insure something that can be used for fraudulent activity. So I said to myself, "FINE! It's going on the plane with me when I go visit him." Well, not fine, actually. As my trip approaches, I'm really scared that I'm going to get questioned at US customs as to why I have his passport. So, the question is, am I able to carry his passport with me? Is it just a common misconception that you can't be in possession of someone else's passport no matter what? I'm not using it for anything. It's just being returned to him, after all! Thanks! I chose UPS because it's the only local shipping company other than Canada Post. They said that because I am declaring it as being a Passport, my boyfriend would have to go and pick it up at the UPS store closest to him and show some ID and deal with Customs and Immigration. I figured that if UPS was going to do this to him, it would just be easiest to take his passport in my carry on and save myself however much it would have been to send it.
Packing & Preparation - 2 Answers
Random Answers, Critics, Comments, Opinions :
1 :
I don't see a problem as long you do not act illegally by misusing his passport. Yes, you may encounter some questions and delay, if you are having his passport in your hand while you present yours. Also consider sending it via Fedex. Use their special envelope and do not have it "dropped" in other words have it delivered to a person at the address given -you must specifically request this-.
2 :
First of all, as long as you are Not using the Passport, they will not are that you are bringing it back to him after he left it by accident!!! Second, why did you not just send it back via Certified Mail. It is even more secure than just insuring!!!