Friend, you will have to give us more to go on. You haven't told us much more than "one clown fish always dies".
When I got into the hobby about 20 years ago, I started with a pair of Tomato clowns, and I still have them. So it is likely something in your process.
Lets start with your setup. A picture can tell us a lot. If you would, please post a few full tank pictures from different angles. Also, pictures of the fish provide good information too.
Do you test your water? If so, please post your latest test results.
Generally speaking, Clown fish can become extremely aggressive, and at times, violent, when establishing who will be the dominant female of the pair and who will be the male. I know people who have lost a Clown fish during this.
Another thing about Clown fish; they are very territorial, particularly when they are protecting eggs; they will attack your hands.
In the end, Clown fish can be real jerks, so, that may be the problem.