Just do it as soon as possible. The longer you go with it the worse it will be.

As he is in love, he will be destroyed. There really isn't much you can do about that.

Also, you better not count on the "friends" thing anymore, or at least not for a long, long time. This person will need a lot of time and space.

Hopefully in the long run, things may improve. Perhaps some day you two will be able to have some cordial relationship. You'll just have to cross your fingers and go with the flow.