off and on

occasionally, sometimes, now and then, intermittently

Adverb
1. not regularly; "they phone each other off and on"
(synonym) on and off

Adjective
1. intermittently stopping and starting; "fitful (or interrupted) sleep"; "off-and-on static"
(synonym) fitful, interrupted, off-and-on(a)
(similar) broken

occasionally He`s been seeing the woman off and on but I don`t think that their relationship is very serious.

Synonyms and related words:
alternately, at irregular intervals, at random, back and forth, backward and forward, backwards and forwards, brokenly, by catches, by fits, by jerks, by snatches, by turns, capriciously, changeably, desultorily, disconnectedly, discontinuously, eccentrically, erratically, every other, fitfully, haltingly, hitch and hike, in and out, in rotation, in snatches, in spots, in turns, inconstantly, intermittently, irregularly, jerkily, lurchingly, make and break, nonuniformly, on and off, patchily, reciprocally, ride and tie, roughly, round and round, seesaw, shuttlewise, spasmodically, sporadically, spottily, to and fro, turn about, uncertainly, unevenly, unmethodically, unpredictably, unrhythmically, unsteadfastly, unsteadily, unsystematically, up and down, variably, waveringly, whimsically, wobblingly
  

adv. บางคราว, บางครั้ง, บางโอกาส, บางเวลา (syn. now and again, now and then)