The dilemma I’ve always had a close relationship with my dad despite not living with him since my parents’ divorce when I was a baby. He’s been through some difficult times over the past decade, coping with bereavement, financial troubles and addiction (his own and that of close relatives). He now lives with his own father to help care for him. For five years, he’s had an on-off relationship with a woman who I now can’t stand. She expects him to pay for her, despite his money worries. When my dad leaves her, she continually messages him or shows up at – or breaks into – the house. He tells me the insane stuff she did during their relationship, then they get back together. Repeatedly he’s promised he won’t go back to her, only to do so. I understand I can’t control who my dad associates with. I know he is to blame as well as her, but I feel if he weren’t so vulnerable he would not have given into her persistence. Could you give me a way to come to terms with this so I can be in the same room as her without my blood boiling?

Mariella replies How about looking at the situation through her lens? I’m not exonerating her of responsibility for her part in your dad’s dysfunctional behaviour, but it’s a common impulse to blame the other party. I once had an almost surreal conversation with a woman whose husband had left her and two young children, unceremoniously, for a more glamorous option – and listened to her fervently blame the other woman. Hooking up with someone else’s husband is not the most sisterly choice, but dumping your wife and children seems to me far more reprehensible. When I tried to reason that this other woman was a stranger with no responsibility to her, while the opposite was true of her ex, she looked at me as if I’d lost my mind. I’m sure there are plenty of other abandoned lovers out there who’ll think me equally misguided, but I’m all for apportioning blame where it should rightfully fall.

So where does that leave us with your father’s girlfriend? You say you have always been close, but sometimes shared intimacy can be the enemy of clarity. You sound protective of your parent and whether manipulatively or naively he appears to be exploiting your loyalty. When it comes to how he spends his money, or why he keeps rekindling his relationship with this woman, you have only his side of the story. It’s clearly more nuanced than he maintains if, after her repeated “insane” behaviour, he keeps giving her re-entry to his life. I’m certain that if you asked for her version of events you’d get an altogether different picture. That doesn’t make her right, or nice, or someone you want to befriend, but it certainly means her actions are wide open to misinterpretation. Meanwhile, your dad has positioned himself where he seemingly feels at home, sandwiched between two women vying for his attention. Whatever the ins and outs of their relationship, its on-again, off-again nature confirms its volatility – and nobody is forcing him to play that game.

He’s an adult, who bears responsibility for bringing you into the world and, one hopes, would have your best interests at heart for his lifetime. My feeling is that he’s negating parental responsibility by confessing intimate and inappropriate details of his relationship seemingly in the pursuit of pity from his daughter. Maybe your relationship with your father is the one that’s most urgently in need of an upgrade.

His inability to maintain boundaries is likely to be propelling him back into this liaison. So teaching him where he needs to draw the line with you would be a valuable lesson. Your sympathy is admirable, but how about putting it to one side and assessing his behaviour on the basis of its impact on you? It’s certainly worth letting him know that your role as his confessor is having a destructive impact on your tolerance of his girlfriend. It’s not helpful to any of you that you’re so immersed in their romantic wrangles, and curtailing your exposure seems the best way to restore civility and sense to proceedings. If adults can’t behave like adults then their offspring often have to. I appreciate you are a grown-up yourself, but that doesn’t mean your parents’ problems, particularly of a romantic nature, should become yours.

You present your father as a complex individual struggling against heightened odds, but he needs to take responsibility for his own destiny. Your sympathy and desire to protect him won’t solve the challenges he needs to confront. This relationship, dysfunctional as it may be, clearly provides something he finds irresistible. It may be better for both of you that you aren’t illuminated on what it is! How freely he spends his money, why they fight and how she reacts when tensions are high are all details open to interpretation.

There’s nothing you can do about their relationship aside from ensure that you’re not a listening ear only open to one channel. The less you know, the more tolerant you can be and ultimately that’s what family is for. I suggest you step back, focus on your own life and in future encourage your father to do likewise.

If you have a dilemma, send a brief email to mariella.frostrup@observer.co.uk. Follow her on Twitter @mariellaf1