The comitatus relationship refers to the beneficial relationship between a ruler and his citizens - he would provide them with benefits, whereas they would provide him with something in return, usually protection.
There is a comitatus relationship between Beowulf and King Hrothgar - he called Beowulf to come to his aid when the monster Grendel started attacking his home and people, and Beowulf responded to his call. When he manages to kill the monster, he gets appraisal and acclaim, and Hrothgar gets the protection he wanted.
However, we can also see comitatus between Beowulf and his men - he grants them recognition and heroism, whereas they give him their loyalty and strength. So any type of relationship where both parties gain something can be considered comitatus in the Anglo-Saxon times.