Denny/Izzie? What even was that

I am rewatching GA from the start and the whole Denny/Izzie thing is so bizarre to watch in 2024. I remember it being an extremely heart wrenching tragedy when I first watched it. But now I am so stuck on how unethical and illogical the relationship(if you can even call it) was. Isn't not falling for a patient a pretty basic rule among doctors? And Izzie really struggled to be where she was so how could she just forget all that? Why did her friends who were doctors not stop her? Especially Meredith, I think she was one of the first ones to figure out what's happening. So many boundaries crossed. So many consistent bad decisions. Don't come at me please.