StageFormGrammar and meaning
1بَاعَدْتُهُForm III past; 'I' subject, 'him' object
2فَـConnects result to the prior action
3تَبَاعَدَForm VI past; he moved away
The important feature is the realisation of an effect following the first action. The former object becomes the person undergoing the resultant state, with no new direct object expressed in تَبَاعَدَ.