In animeland "mothercon" is sometimes used to mean "Oedipus complex", but here (especially with the definition given by Mohawk) it just means the normal real-world use of someone being overly attached to their mother (the usual standard being someone who's more inclined to listen to their mother than their girlfriend/significant other). Mama's boy/Momma's boy is the closest equivalent.
Though that does mean I have to edit post #4477857, because I already used that term for "can't be weaned" (which also has a similar meaning).