i think it is more accurate as a very light surface level of jealousy which is more of he wanted to be the only one able to see her like this and eat her food etc. for a bit longer, so more like didnt wanna share kinda thing
the title is lie: he's not jealous. he just wants their secret to last longer, for Mahiru's sake. tho... he IS down bad for Mahiru most of the time, sooo... i guess the title has SOME truth to it lol
The LN and WN both are actually pretty good except 2 annoying characters- Amane's Mother and Chitose. It would have been 100x better and more enjoyable if those 2 annoying characters were not there.