Dueling with a life-long friend is a more emotionally grueling experience than dueling with a long-lost father with whom you have never had a relationship.
They were friends? It never seemed that way.
I always got the sense that they were friends. I think the central problem with the prequel trilogy - other than Jar Jar - is the fact that George Lucas gave what was supposed to be Obi-Wan’s role to Qui-Gon in Episode I, which should have clearly established Obi-Wan and Anakin’s relationship.
It is still evident that they are friends from the scene in the elevator in Episode II, the clone wars series, and the beginning of Episode III. It is important to remember that Obi-Wan never heard Anakin speaking negatively of him to Padmé, so from Obi-Wan’s perspective they were definitely friends even if they fought at times.