Every time bill finds himself in a romantic situation with his partner, he finds that the slightest provocative action on the part of his partner, such as a caress or a lingering kiss, causes a sudden, rapid ejaculation. bill most likely suffers from

Bill most likely suffers from premature ejaculation.
This means that he is easily aroused without even much stimulation - in his case, even the slightest caress or a kiss can cause him not only to become extremely aroused, but also to ejaculate. Premature ejaculation occurs really fast, before the person wants it to happen - it is an involuntary action.