Seems the ML is special forces because of some special ability that increases his overall abilities, but also occasionally turns him beserk mode. This ability hurt the MC when they were young. ML forgot all about MC in his guilt.
MC does have feelings for ML all along, but refuses to respond to ML until he remembers their childhood. He also think ML betrayed his feelings by falling for the MC's older brother.
MC studied physics [why physics and not medicine I'll never know] to stabilize his lover's condition.