If you end a relationship, do so with kindness and respect.
Let your friend know that you have concerns, that you've given it thought, and that you believe it's the right decision for you.
Sometimes we come across someone who we find incredibly amazing.
He meets several, if not exceeds the expectations we had for a mate.
Share the concerns if your friend would like to know, but address them as behaviors, not traits. You might get promises, begging, or anger from your friend.
If you end the relationship now, it doesn't necessarily mean that reconciliation may not happen down the road.
Either of you, short of the altar, may decide against the relationship.