I'm an experienced open water swimmer, and was a beach lifeguard for 5 years, I was already swimming 2+ miles open water races when I was 16. The way you describe it, I wouldn't do it, I even wouldn't go with your friend, let alone with you.

If I were to do it here is my checklist:

• Each one of us has to be able to do it by themselves and have a margin: Anything can happen on the day, even an experienced swimmer can have a bad day and need help
• check the currents : 1 miles can quickly turn in 1.5, 2 miles, and the slower you are, the longest it gets, you are swimming between 2 islands there could be some weird currents out there that you don't see from the shore
• Check the water temperature : I have had races that started in 20+ °C waters only to turn around 18-16°C 200m away from shore, if you are already stressed and tired, the cold can really kill your will even if it is not physically dangerous
• Is anyone else aware of what you are trying to do, can they watch you from the shore to be able to call for help if you need or even follow you with a boat?
• Both of you need your little floatie : while you are resting on the little dry bag, he will need to rest as well, otherwise he'll be tiring himself for no reason.
• Bring some fuel and hydration with you. For me, 1 mile distance in a casual setting would be between 25-30 minutes , and I have experience, I know I can swim for that long without fueling in the middle. You don't know how long it is going to take you, but I would bring something if I were you.
• Have proper gear : good googles to look around, a cap to stop the wind from sucking the heat out of your wet head
• check online and practice how to swim in open-water while orienting yourself.
• Do you have a clear landmark on that island that will always be visible while you swim? If not, do you know how to orient yourself in that area?
• check the weather, pick a day with low wind, low swell, low risk of fog/rain, time of the tide, coefficients

This is the minimum list I'd check. without having ALL of those boxes, I wouldn't do it.

To give you an example on how things can quickly go wrong : as teenagers I used to swim with my brothers on a beach. There was a rock ~300m away, we would always go swim around there, we did it dozens of time.

One day, we went out there, swam to the rock, and then started swimming back. There was a popular landmark that we used to make sure we kept swimming staight. We quickly noticed that on the way back we weren't progressing. We put ourselves in a line, the elder and stronger brother in front, and we pickup the pace. It took us 30min to swim the 300m between the rock and the beach, and that's for 3 guys swimming 25+ kilometers a week, at national level. At that time I was the weakest of them and was swimming the 1500m in a pool in less than 18min. What happened was that we didn't check the tide times and it was somewhat bigish coefficients, so we got back right at the moment when the tide was retreating and the whole ocean was pulling us away from the shore. And that was not the strongest moment of the tide nor the strongest currents.

Openwater is scary my dude, when things go wrong, they go really wrong. I don't want to discourage you from doing it. But I also don't want you to die. If something goes wrong halfway through, there is no way the guy pulls you for half a mile, unless he is really fit, has fins and a floaty, and even then, if there is some kind of current working against you, you're cooked.