I have gone back and forth about posting this because I know people will have strong opinions, but I genuinely don't know whether I've completely lost perspective.
I am 36 and have been seeing my sister's ex husband, who is 44, for just over a year.
Before anyone asks, there was absolutely no overlap. They divorced several years before anything happened between us. They never had children together and have had very little contact since the divorce. My sister has since remarried has three children with her husband and from everything I can see is very happy.
The reason I'm struggling is because, regardless of all of that, I know how this looks.
It started completely unexpectedly. Around this time last year we both happened to be at the same event through mutual friends. I hadn't seen him properly in years. We'd exchanged the odd polite hello over the years but after the divorce there wasn't really any reason for us to see one another.
We ended up talking for most of the evening. It wasn't flirtatious to begin with. We just clicked. We spoke about work, family, relationships, life after divorce and all sorts of things. It felt incredibly easy, which surprised both of us.
At the end of the evening we carried on talking over another drink and, before I knew it, we ended up sleeping together. I just thought it would be a one night stand.
I woke up the following morning convinced it had been a mistake. I remember thinking I'd probably never hear from him again and perhaps that was for the best.
Instead, he texted me later that day to make sure I'd got home safely. A couple of weeks later we met for coffee intending just to clear the air. That turned into dinner then seeing each other every few weeks, then every weekend we could manage.
Somewhere along the way it stopped feeling like two people casually spending time together and started feeling like a relationship.
We've now been together for over a year.
He's genuinely one of the kindest, calmest people I've ever been with. We have similar values, similar interests and neither of us feels the need for games or drama. It has been one of the healthiest relationships I've ever had, which only makes the situation more complicated.
The problem is that everyone within my immediate family thinks I’m single.
A couple of close friends know, and his friends all know about us now but nobody in my family has any idea. My sister certainly doesn't.
Up until recently we have both been happy to keep things private while we figured out whether this had a future.
Now he says it does.
A few weeks ago he sat me down and said he doesn't want to keep pretending this is casual anymore. He wants us to have a proper future together and has started talking about marriage.He also asked me whether I still wanted children.I laughed and said that yes, ideally I would, but I'm 36 now and very aware that time isn't exactly standing still.
Then I remembered my sister had all three of her children between the ages of 39 and 42, so perhaps I'm worrying more than I need to and if no children then I have always been open to adopting
What has really shaken me is that I can actually picture that future with him.
I've been engaged twice before and on both occasions I ended the relationships as realised I couldn't go through with marriage. I said no because, deep down, something never felt quite right. As difficult as those decisions were, I knew I wasn't marrying the right person.
This time feels completely different.
For the first time in my life I can genuinely imagine marrying someone without hesitation. I can picture us growing old together. I can picture having children with him if we're lucky enough for that to happen.
And that is exactly what makes me feel so dreadful.
The one man I can honestly see myself building that life with is my sister's ex husband.
It almost feels cruel that this is the situation I've found myself in because, if he were anyone else, there wouldn't even be a decision to make.
It made me realise that this relationship is no longer some secret that might quietly fade away. We're talking about real life decisions now.If we're discussing marriage and children, we can't hide forever.
He has said he doesn't want to be anyone's secret. I completely understand that. If I genuinely see a future with him, I don't think it's fair to keep asking him to pretend he isn't part of my life.
The problem is my family.
I genuinely don't think my sister still has feelings for him. She's happily remarried, has a lovely family.
But I also know this isn't really about whether she's over him. It’s selfish of me.
It's about the fact that he's her ex husband.
I'm terrified she'll see it as a betrayal by me rather than by him. I worry she'll question whether I'd always had feelings for him, which simply isn't true.
I'm also worried about the wider family. I can already imagine awkward Christmases, people taking sides.
At the same time, we're two single adults who met again years after a marriage had ended. There were no children involved in their marriage, no ongoing ties beyond the fact they used to be married, and they've both built completely separate lives.
Part of me thinks life is too short to walk away from someone I genuinely love because of what other people might think.The other part of me wonders whether there are just some lines you don't cross, however much time has passed.
I honestly don't know what the right thing to do is anymore.
So, AIBU for thinking that, given they're long divorced, had no children together and she's happily remarried, I should keep pursuing this relationship? Or is this one of those situations where, no matter how much time has passed, your sibling's ex husband should always be off limits?