If you had a step-mother and a mother at the same time, you would pay attention to your step-mother but nevertheless your constant recourse would be to your mother. That is now how it is with the Court and philosophy. So return to philosophy again and again, and take your comfort in her: she will make the other life seem bearable to you, and you bearable in it.
Similar to his meditation in B5:9, we should always get back up when we fall. I particularly like how he doesn't seem to get upset with himself. There is no swearing or self-berating. He simply councils himself to "return" and get back into the good groove. We approach "getting back up on the horse" like practicing anything else. We practice playing an instrument to perform better. We practice a sport to play better. We practice returning to stoicism to live better.
It seems to me, in the next passage, Marcus alludes that his "step-mother ... the Court" distresses him, and therefore the advice to "quickly return to [himself]" or his true compass - his "mother ... philosophy." This sentiment rings so true with me. Learning and attempting to practice stoicism helps me through the day when I go to work, or deal with commuting, or talk with people who have poor customer service skills and or work with people whose brains are still developing. It helps me have patience with getting my home back in order after a major flood. It helps me to manage the anxiety from mistakes I've made. And at the beginning and end of the day, and sometimes during the day, I return to "mother - philosophy" and she reminds me what I'm aiming for.
(see also Citadel p. 29, 291)