Welcome. Post #1 I see.
Your friend is right - you want your front sight to be in focus, whether you shoot with one eye or two. You are always going to see some things double with both eyes open, but you can train your brain to ignore the "ghost" image with some practice. I would suggest putting a piece of scotch tape on your eye pro lens of your non-dominant eye. That may help your dominant eye "take charge" and make it easier for you to focus on the "real" image, and not the double targets.
Switching between one eye open and one eye closed while looking at the same target can be helpful. Put a target up on the wall and just do a dry fire "focal shift" looking at your target then moving your focus to the front sight, and back to the target, etc. Try it at different distances, with different sized targets. It can become more difficult when you have a few similar targets side by side and the "ghost" images all blend together.
I'll let you in on one more secret - while it's best to be able to shoot with both eyes open, it's not an absolute requirement. It gives you a better field of view, that's about it. There are plenty of GM IPSC shooters who shoot with one eye open. I personally will move between one eye open or both eyes open depending on the target, distance, lighting, etc. With good lighting, outdoors, I'll keep both eyes open all the way out to 100 yards. Indoors, with poor lighting, I usually have to close one eye once I get out past 20 yards or so.