The past tense of fall head over heels in love with is fell head over heels in love with.
The third-person singular simple present indicative form of fall head over heels in love with is falls head over heels in love with.
The present participle of fall head over heels in love with is falling head over heels in love with.
The past participle of fall head over heels in love with is fallen head over heels in love with.