As long as you tell the story in a poignant and respectful manner, I don't think there's a significant problem. But if you're still not sure about it, I think I'd just take this as a case study of sorts and write down what details you think make this a compelling conflict. Maybe look into other, more anonymous marital troubles and how they work, (there's no shortage of that shit on Reddit) until you think you've found the right bits and pieces to make something like this that is suitably your own creation. If your friend is, say, Richard Nixon, you don't have to write a story about watergate. But if the concept interests you, learning more about the politics of the time can help you fabricate your own watergate-adjacent conflict that's fictional enough for you not to offend your friend.