Hell, if she'd been there NOT as his friend it would have gone better for her and him both.
A not-friend wouldn't have blown up at him having a PTSD attack but handled it professionally.
If you're having doubts that someone is not functioning "professionally", why would you bring up your "relationship" details from the past AND then sleep with them unless your intent is to catch them with their pants down (so to speak).
Lorca is NOT behaving normally, but let us not forget that Cornwell doesn't have clean hands either (tardigrade experiments anyone?)