The following rant is full of spoilers for LoT s2ep05
HE COULDN’T SAY IT HE COULDN’T SAY HE HAD FEELINGS.
He had extreme feelings for Len. he cared so much and seeing Ray in the jacket was too much for him. Mick gave him the gun because he thought Ray was ready.
Mick wanted Len back so much he was trying to change Ray but then he saw that Ray needs to be Ray.
MICK HAS FEELINGS PEOPLE! FEELINGS!!