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Fans of the movie “My Best Friend’s Wedding” will be familiar with the pact the two main characters make—they’re best friends who promise that if they’re both still single at 28, they’ll marry each other. Most people today can agree that that’s jumping the gun a little bit. A lot of people are still single at age 28. Millennials in particular are postponing a lot of things—serious relationships, marriage, career path commitment, and children. And they have good reasons. So while the age detailed in that pact may seem unrealistic, the spirit of it may be something a lot of people understand. In fact, I know friends who’ve agreed to marry each other if they’re both still single at 40. And while that is, admittedly, a more reasonable age than 28, there are still a lot of reasons this type of pact never works out.

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You’ve slept with his friends
By age 40, if you’ve been hanging with this friend and his friends enough, you’re bound to have hooked up with and even dated some of his buddies. That will make things pretty awkward if you marry him.

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He’s slept with your friends
Oh, and he’s slept with some of your friends. It would just be weird to marry someone whom three of your good friends slept with.

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You’re friends with his exes
If he is divorced or was with another woman for a very long time, you naturally developed a friendship with her—a friendship that still exists. Imagine how betrayed she’ll feel when you marry her ex.

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He’s friends with your exes
If you were ever married or in a long-term relationship, your friend probably befriended your ex. That ex will be very pissed if this man marries you now. And sometimes when men get mad, they throw punches.

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You know his flaws deeply
You’ve watched him make the same mistakes over and over again in relationships. You know exactly why he’s single—and he isn’t faultless. Are you really going to buy a product that you know is so dysfunctional?

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Forty is actually young to give up
Even 40 is a bit young to just give up on marrying someone you actually love and are excited about spending your life with. That’s the new 30! You still have a lot of good years left to find the one—the real one.

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That pact angers your exes
Oh and by the way, before 40 arrives—like during your twenties and thirties—the other people you date find out about this pact and it makes then pretty upset. If the tables were turned, wouldn’t you be upset if your boyfriend had a pact to marry someone else?

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You know too much
You’re friends so, within the trust of friendship, he told you all about his sexual experiences over the years—all the nitty gritty. It just isn’t natural to marry someone and have all those images in your head about his past sexual encounters.

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Someone is pining after someone else
While you may both be single at 40, it’s still quite possible that one of you is pining after someone else—trying to make it happen elsewhere, with someone else.

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You can’t force sexual chemistry
You just can’t force sexual chemistry. Trying to have sex with someone you aren’t into will just…traumatize you.

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You may hook up before that
Or, maybe you already slept with this friend. Hey, that will happen between a man and woman who are friends for decades. So if there have already been sexual encounters, then adding a marriage actually makes the pact feel even more serious. It’s too real—it’s not just about companionship at that point.

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Nobody wants to move
For the record, neither of you will want to move out of your place into the other person’s, or into a new house. By age 40, you’re pretty nested into your bachelor/bachelorette pad. Only real love motivates you to change habitats.

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You could be mid-divorce
The thirties are a common age for someone to go through a divorce. That means that, while that pact is coming up, one person (or both) may still be wrapping up a divorce.

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Or onto your second marriage
Or, they may miss the window. Someone could be onto their second marriage by age 40, leaving the other one in the dust.

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So timing never works out
Either way, it’s highly unlikely that the timing will work out. If both individuals are single at the same time, it may be at age 70, and by that time, neither wants to bother with marriage.