Dear Sian,
I am not sure what the extent of hurt is upon you. Criticisms, put-downs, disrespect are some reasons why you may want to put a distance to protect yourself. However, if you find that the friendship is lacking in consideration of your needs, perhaps your friends are not good listeners, and it can be a matter of personality differences, or self-centredness. Like two sides of a coin, I hope the positive aspects of the friendship outweighs the negative aspects.
With most relationships, there tend to be ups and downs, better days and not so good days. Even close family members do hurt one another sometimes because people are not perfect. Others may have hurt us with their actions and words; unknowingly, we too, may have done the same towards them.
The fact that you have been best friends from secondary school years speaks volumes of the resilience in your friendship. In addition, you mentioned that they love you, would not badmouth you and would apologise to you. These are positive aspects to focus on. Scripture exalts that a friend loves at all times (Proverbs 17:17a). Friends are to encourage one another, build oneanother up (1 Thessalonians 5:11), to bear with one another and forgive one another of grievances (Colossians 3:13). May these acts of love be found mutual in your friendship to them and vice versa.