Why would boy go to great lengths to show his interests if he is going to dump her?

i've known this boy for 6 months now and had some special time(s) wiht him in the beginning until about 2 months ago. when he was did a real jerk off thing! during last 3 wks he sucked me in again in a dishonest kind of way and i truly believed every thing he said. Gullible? yes. however, i didnt feel i had any reason to disbelieve him. we share a common ground uncommon to others and we have since we very first met and it seems he knew about it before we met. why would he go to these extreme lengths? please explain and im looking for 'honest' answers