Learn English – Idiom or expression that would imply “someone is showing equivocal behaviors that indicate a feigned reluctance”

Cuckquean is the word you need, a female cuckold (cuckold being the more common word for wittol).

Cuckquean refers to a woman with an adulterous husband. In modern English it generally refers to the sexual fetish in which sexual gratification is gained from maintenance or observation of sexual relations by a man with a woman or a number of women besides his girlfriend, wife or long-term female sex partner, and therefore, the reversed gender roles of a cuckold relationship.

Sadly there is a Wikipedia page so probably counts as sort of general reference.

But to make it a little less general reference I could add some other stuff...

While cuckold and cuckquean are not directly related to the word cuck (passing excrement, shit) as such, the term cucking-stool (corrupted to ducking-stool) has also been called the coqueene-stool and the cockqueane-stool.

OED says of the cucking-stool:

An instrument of punishment formerly in use for scolds, disorderly women, fraudulent tradespeople, etc., consisting of a chair (sometimes in the form of a close-stool), in which the offender was fastened and exposed to the jeers of the bystanders, or conveyed to a pond or river and ducked.

Seems to me that a cucking-stool is more than a dip in the river. If I can find anything ruder or more vulgar I'll add it in.

_{Wikipedia contributors, "Cuckquean," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Cuckquean&oldid=641764807 (accessed February 9, 2015).}

You might say,

She/he isn't your cross to bear. Ditch him/her/Cut all ties with him/her now or you might regret it for the rest of your life.

bear one's cross and carry one's cross

Fig. to handle or cope with one's burden; to endure one's difficulties. (This is a biblical theme. It is always used figuratively except in the biblical context.) It's a very painful disease, but I'll bear my cross. I can't help you with it. You'll just have to carry your own cross. McGraw-Hill Dictionary of American Idioms and Phrasal Verbs

ditch

: to stop having or using (something you no longer want or need) : to get rid of (something)

: to end a relationship with (someone)

: to get away from (someone you do not want to be with) without saying that you are leaving

(Merriam-Webster)

cut/break (all) ties with (someone)

To end or discontinue a relationship—romantic or otherwise—with someone or some group. Mary cut all ties with her family when she moved to New York City. The government began cutting ties with the war-torn country after its human rights atrocities came to light. Farlex Dictionary of Idioms

[leave] that guy/girl before he/she spells trouble for you

spell trouble

To be the cause of possible problems in the future (often + for)

Cambridge Idioms Dictionary, 2nd ed.