I read your detailed description of your boyfriend's issues & bump behind the ear!
From all acoounts it appears to be an infected sebaceous cyst
or a cyst that was traumatised with a hematoma
(blood clot) & secondary infection.
In either case, the definitive treatment is Excision surgery under local aaesthesia done by a general surgeon
or an ENT specialist
or even a dermatosurgeon. It is a minor procedure & easily remedied.
Good Luck & Godspeed!
Dr Praveen Rodrigues MD