yup ,this is all on his mind (ofc there are also people and factors that always upset him and make him doubt about Jesse) but his own mind is the root of everything.. this is like compulsive disorder and this is getting worse with the passage of time.
*spoiler*
Even when Jesse will open a bit of his heart to him at some point (in the future)
Law's mind is too fragile..There will always be things or people who make him doubt or image things about Jesse. :(
Meant to hit like
Wahhh now you're making me so curious >.< I wanna knooow~
Damn all this waiting is killing me ┗( T﹏T )┛
And so the seeds of insanity take root in his mind...