We all know the saying, "it's better to have loved and lost than to never have loved at all." But do you believe in that? If you knew it was going to end badly, with your heart broken, would you avoid the relationship to begin with?
Oh God, you can do a lot with hindsight, can't you? Dealing with a truly-broken heart is a very painful process. I suppose it depends on how badly it ended, especially if you had both invested a lot of time and energy in the relationship.
I have a feeling that if I knew that things were going to end badly, I would steer clear of the relationship and indeed have done so in the past.