The dilemma When I met my husband, it was love at first sight. He was married, with an 18-year-old son, but left his wife soon after. Three years later we married and spent nearly 30 happy years together. During the last six years his health deteriorated, and he died two years ago. His first wife remained very bitter towards both of us, but more so to me. My husband and I did not have children, so I continued to work for almost 40 years without a break. Consequently, I now have a reasonable income. I own my home and, having recently reverted to working part-time, have an income, my pension and a small pension from my husband's employment. My husband's first wife lives in more straitened circumstances. He had maintained a monthly financial contribution to her which, according to a private agreement, ceased on his death. Should I continue to honour this? I don't know if this is a moral or ethical dilemma, or am I trying to assuage the guilt I still feel after all these years?

Mariella replies Probably the latter, but does it matter? Whatever your reasoning, you've restored my faith in human nature. My more regular correspondence from women who've been in your position and fallen for committed men tends to be self-justifying. I'm used to letters from angry second wives resentful that their predecessor won't accept her husband slipping away, without a fight, into their eager arms. If I had a pound for every woman who has ever told me that their partner's ex was money grabbing or frigid, unsupportive or irrationally angry, a workaholic or a total couch potato and, of course, that the relationship was long over and his moving on hardly a surprise, I'd have retired from the agony game to spend my millions.

The absence of shades of grey in such missives is evidence of the desperate desire in such complicated emotional terrain to shake off any responsibility for a relationship's demise. I'm not saying that there should be flood levels of guilt just because you fall in love with someone who'd promised themselves elsewhere. Every adult has the right to choose who they wish to spend their lives with, and we're all capable of making mistakes, but no one escapes with their self-regard intact.

It's amazing how many sane and lucid members of my sex lose all sense of reason when attempting to exonerate themselves from their part in proceedings. It would be so refreshing to hear people admit that, as with a car or item of clothing, they saw a person, wanted them and, after time, effort and emotional wear and tear, got them. Instead we have to listen to a series of their presumed rivals' alleged crimes, each one less believable than the last, until all credibility is lost.

A friend once told me in all seriousness that her married lover and his wife hadn't had sex for the preceding six years except on two occasions, when he'd been lured against his will. She knew it was only twice because each time, in this harridan's efforts to hang on to her spouse, she'd managed to get pregnant! Pointing out that this man's wife had to be one of the most fertile women on the planet didn't endear me to my incensed and wholly indignant girlfriend.

We inhabit a world where we're taught that we can have what we desire, and tend to act on it – the least we can do is admit to it when we succumb to our instincts. Finding ourselves drawn to someone who is committed elsewhere, it's our duty to confess that our passion obliterated any sense of fairness. We just had to have them. Then we'd be dealing in far more honest currency than that of the litany of blame hurled by strangers at strangers just because a mutual lover has come between them.

Normally if I display partiality it's firmly on the side of my fellow females, but in those circumstances I feel such irrational tendencies can't be condoned and deserve to be highlighted. Thankfully for you, that emotional quagmire lies far in your past, but to your credit you haven't forgotten it, or the cost paid for your happiness. This man's first wife may well have been the architect of her own misfortune, but until recently pension laws discriminated against first wives in such a scenario, many of whom were housewives.

You have absolutely no obligation to continue the support of your late husband's ex, and there are very few among us who would contemplate doing so. Already impressed by your work ethic, the financial security you've created for yourself, and the magnanimity you display toward your predecessor, I would recommend you for sainthood were you to actually go through with it. It's certainly a lovely thought.

If you have a dilemma, send a brief email to mariella.frostrup@observer.co.uk. To have your say on this week's column, go to theguardian.com/dearmariella. Follow Mariella on Twitter @mariellaf1