What is the ruling on ending a friendship with those who only accept (you) when they are in need and cause much annoyance, and is mentioning their harm by way of complaint considered backbiting?

The basic rule is the prohibition of a Muslim abandoning his brother for more than three nights. An exception to this is when association brings harm in matters of religion or worldly affairs. If friendship with them causes harm, then association with them can be reduced. As for mentioning their harmfulness in front of people, it is backbiting (gheebah), which is forbidden, unless it is in the form of a complaint to achieve a considered benefit or avert a harm.