The dilemma I have two ex-wives: two children with one, and another child with the other. I see my children all the time, have never missed child support payments, attend events and help as much as I can. My relationship with my second ex is strong, but not with my first. I’ve recently begun a new relationship with someone who has a young son. I am really happy and treat him as my own. I completely love them both and think I am finally content. She has met my children although we have not stated we are partners. My second ex is happy for me. My first ex, however, has banned me from going anywhere with my new partner when I have the older two children. It has meant we have missed family events and my partner doesn’t get to know my older children. If I try to stand up to my first ex she becomes abusive and brings up our break-up, which was more than seven years ago. I don’t know what to do. If I put my new partner first I get accused of neglect; if I play nice with my first ex she takes advantage.

Mariella replies That’s quite a lot about you. I do, however, appreciate irrepressible optimism. And your assertion that you have now, finally, found the woman who will make you content is certainly that. You’re not alone in your struggle to create harmony between family left behind and those you move on to. It’s an increasingly necessary life skill as longer lifespans and the hunt for personal happiness takes its toll.

You may be a pioneer of this new phenomenon, but your quest for a companion who will make you feel good, coupled with support from all those you’ve lingered with along the way, isn’t inspiring my sympathy. Instead, with you putting “I think” in sentences about this new relationship’s potential I find myself lurching toward your first ex-wife’s corner.

It’s not that you should be held to ransom for past mistakes: of course that does none of us any good, but it could be that she has less conviction about the lasting potential of what’s heading to be marriage number three than you do. The benefit of hindsight is a valuable gift. Judging by your allusion to dates you’ve managed two wives and three children in less than a decade. No wonder your first incumbent has little confidence that this latest fancy will be any more of a permanent fixture than she or her replacement were.

Putting children through the turmoil of embracing new partners is unavoidable, but it’s often prematurely demanded to assuage a parent’s guilt. That’s why far from being included in the auditioning process it’s better in most cases that the relationship is firmly cemented before you reinvent “family occasions” to include new arrivals.

You say you’ve started seeing this woman recently and I’m curious as to how “recently” you mean. The enthusiasm to introduce new lovers to friends and wider family is a perfectly natural impulse, but when it comes to kids a more cautious approach is preferable. So why don’t you make the most of this enjoyable liaison and also of the precious time you have with your own children without trying to create a Kardashian family clan?

You say you “help” with your children “when you can” – a luxury not many parents enjoy – and I can’t shake off a suspicion that you’re pretty focused on you. Look at all the “I”s in your email, for starters. So how many potential stepmothers do you expect your children to meet and get to know? Does ex-wife number one get on with ex-wife number two? And does your love for the latest youngster caught in the slipstream transcend what you feel for the child’s mother? In other words is your current devotion to the boy likely to continue if you and this latest squeeze split up?

The thing about having children is that for as long as they are dependent and vulnerable you can’t reasonably expect to freely follow your heart. Their feelings and indeed their basic human rights must also provide a point of reference. I’m not against you dating, or eternally questing for Mrs Right, but is it absolutely necessary to envelop the children quite so swiftly into the newest family fold?

Choices have repercussions and learning to live with the outcome of your decisions is as important as striving for personal fulfilment. Trying to get three women and four children to sing “Kumbaya” for your pleasure seems a pretty selfish demand.

A harmoniously blended family isn’t your automatic right. Like everything else in life it’s something you have to work for. Your first ex-wife may be unforgiving and guilty of wilfully obstructive behaviour, but you’d be surprised how much you could improve understanding between you simply by changing tack. Listening and understanding, and taking responsibility for the emotional scars you’ve created, will serve you far better than just expecting others to hop to your tune.

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