I'm going to date someone a friend has pined over for years.
Have you told your friend about it?
At first they said they wouldn't be comfortable with it, but I was able to change their mind.
While it is good that your friend changed their mind, you shouldn't date somebody that your friend likes. It could hurt your friendship forever.
They said they were ok with it though.
They may have just said they were ok with it because you were being persistent and they wanted to just move on from the topic. It would be a better choice to simply not date the person at all, unless dating that person is more important than your friendship. It may very well be that you have to choose on or the other.