"If you think it's perfectly fine to stay friends with your ex, you're blind."

On last night’s episode of Married at First Sight, we saw Craig make the very rookie error of bringing his ex to his faux reality TV wedding.

An ex he had been in a relationship with for 13 years.

And this ex was one of what appeared to be about a dozen cherry-picked guests for the ceremony held in New Zealand.

Naturally, Craig's new husband Andy reacted like any normal human being would.

He got pissed off. He labelled it a deal-breaker.

The misery was literally dripping off his face.

Because who the heck brings a long-term ex to such a huge step in a relationship?

Craig and Andy only just met at the altar thanks to the miracle of ~television~ but that surely makes it worse. Because you'd forgive Andy for automatically assuming Craig is either dangerously socially inept or has some heavy baggage he just can't let go.

But not everyone thought Andy was acting rationally.

@Lauhouse @MarriedAU He's attitude is pathetic, what's the big deal about staying friends with a ex boyfriend? shows maturity #dramaqueen

— Kellie Blair Melb (@Misskellieblair) August 31, 2016

And when Andy's mate convinced him he was overreacting, some rejoiced.

This "voice of reason" implores Andy not be so quick to judge, telling him the fact Craig was in a relationship for 13 years shows he is "loyal".

Loyal? Sure, maybe.

Respectful? Definitely not.

It is not OK to thrust that on your partner without warning. Erin from last year's season, has the right idea.

Successfully staying friends with an ex is one of those things many people see as an ultimate social goal. How mature! Admirable! Sensible! If you can achieve that, you can achieve anything!

But if you think your new partner will start popping champagne in celebration of this feat with you, you're wrong.

Deep down they will get a fleeting sense of discomfort; a feeling they are competing, proving their worth next to your ex. And it's not fair to put them in that position — certainly not without being sensitive to the idea there might be consequences emotionally.

This is particularly the case with an ex from a long-term relationship. Someone you spent years with. Someone you had a crapload of lazy weekend sex with. Someone you at one point might have imagined a proper future with. It's not exactly hunky dory.

You broke up with that person for a reason. So why would you want them sticking around? They've served the purpose they were meant to in your life.

I understand sometimes it's more complicated than that, or that you are forced into hanging out with an ex in group situations if you move in similar social circles. That's perfectly fine. But don't go out of your way to be great mates.

Keeping them close sends the wrong message to a new partner.

Even if they insist it's totally 'fiiine'. They are only human, and it's only natural that they could have - no matter how big or small - feelings of jealousy, inadequacy, confusion.

And that's on you. So don't be blind to it.

For the sake of your new relationship, discuss that sticky ex in your life properly. Better yet, let them go.

And for goodness' sake, don't go rogue and invite them to your wedding.