I oni can say that u adi starting to leading urself into trouble.
In this case u dont need to ask him anything because u urself adi set up a statement in ur mind which u tell urself that statement is the only truth, which is u belive that theres is a gal caring "ur bf lips" (which for me this is sl small matter...) and u think that might be ur love rival.
So if he tell u something that is diff from ur statement u will not belive him and u will keep on thinking he is lying.
Seriously, continue wit ur statement can lead to break up.
Dont follow my ex path...

Else, trust what he say and distrust him in ur heart.