Differentials for your boyfriend's case are ureteral and kidney stones, hydrocele, varicocele, a hernia and a hematoma.
I suggest that he seek consult with a urologist for a complete assessment.A urinalysis may rule out possible stones in the urinary tract or an underlying infection. A scrotal ultrasound may be able to ascertain the underlying cause of the lump.Hydrocele and varicocele may present as scrotal lumps. A hydrocele may present as a large pear shaped lump in the scrotum.A varicocele may have a particular feel on palpation. A hernia may enlarge on straining as one increases pressure within the abdomen. This may be true with a varicocele.
Was there any prior injury to the area? A hematoma may present as a bluish lump in the genitalia.
Do keep us posted with regards to your physician's advice.
Turns out he has Retro Spondylolisthesis. Possibly a congenital disorder where his L4 and L5 vertebrae have slipped backwards. This caused exposed nerve roots and muscle spasm radiating up and down his back and groin with numbness in his right foot. The doctor prescribed naproxen for pain and orphenadrine citrate as a muscle relaxer. If the pain continues to get worse he suggested seeing a back specialist for steroid shots and an MRI.