Playing Poker With Your Friends

So last night I was at a real casino playing Poker. My friend and I were on the same table. I was dealt KT and decided to play. My friend was holding AT, but I didn't know that at the time. The flop came AQJ giving me the nut straight, and it ended up being Heads Up with my friend and I. He was looking for a K, but drawing to 3 outs. I was first to act, and when the straight hit, I check-raised him, which he called. Turn was not a King, I check-raised him again, which he called. And then the guy to my left said, "Wow, check-raising your buddy." So the river was a blank again, I checked, he checked and I turned over my straight as I just took about 20$ if not more of his chips (playing 2/4 Limit). All I said was, "It's a tough game."

And then I felt bad because we went to have fun and he was telling me how he was going to triple his stack and whatever else. He ended up losing his stack twice as he bought in again after leaving the table. I tried giving him back the chips I took from him, but the dealer said it was against the rules, which I was not aware of at the time.

What is your take on playing against your friends at the same table?

Do you think I should have just checked through and let the minimum amount of damage be done?