My bff (F31) and I (F29) made a marriage pact

One of my best friends (F31) and I (F29) made a marriage pact in high school, that if we both weren’t married by 40 we would have a “lavender marriage”, and it’s starting to feel real now and it’s worrying me.

We are both straight cis females so this isn’t the typical lavender marriage, but would technically be a marriage of convenience. This marriage pact started out as a joke in high school when talking about how much the guys we knew sucked, and if we couldn’t find a man we liked by 40, we would just get married to each other. I am 100% someone who likes to roll with the bit and make references and jokes frequently, so that’s what I did. I joked about it, and even made a card stating how I wanted her to propose to me. It’s been a frequent thing to bring up, and we tell others about it all the time.

Well, now we’re getting older and these jokes are starting to stress me out because the time is drawing nearer and we both are nowhere near getting married to anyone. Within the past couple years she’s started bringing it up more and more frequently, “when we get married can we do this?” or “when we live together can we get this?”. And at first I thought she was just rolling with the bit, but lately she seems like she’s actually planning it and is quite serious.

She’s told me a few times that she’s saved the card I wrote to her telling her how to propose so that she can use it on the day. She’s been talking more about how it would be a perfect marriage since we can get financial stability from it, get a house together, etc. while still seeing other people.

I honestly always only saw this as a bit, but now I’m getting concerned that she’s quite emotionally invested in this and I don’t know what to do. I thought I’d definitely be married by 40, but as I get older I’m realizing life doesn’t always work out the way you’d expect. Bottom line though is I definitely don’t want to follow through with this marriage pact… I feel like if I bring it up she will be genuinely so disappointed. Which I guess it’s better to bring up now rather than later, but I have no idea how to bring up the topic in a natural way. Any advice on how to go about this? Should I bring it up to her? Or just cross my fingers and hope one of us gets married before then? What do I do?