The trailer for the much anticipated fourth season ofSex Educationwas released a few days ago.With it also came the news that the upcoming season would be the last, as series creatorLaurie Nunnsaidin a letter to fans, “It became clear that this was the right time to graduate.” While this is heartbreaking for fans to hear, it’s also understandable. This season is the moment forSex Educationto come to an end, but not because of anything that might have to do with a dip in quality. The show was as good as ever in Season 3, but cast changes and real life have made it time to say goodbye.

In a surprising and upsetting move, it was announced last year that two ofSex Education’s most loved characters wouldn’t be coming back to the series for the fourth season. Then came news that two more of the show’s most important characters wouldn’t be around much longer either.Sex Educationmight put its main focus on awkward Otis (Asa Butterfield), and his sex therapist mother, Jean (Gillian Anderson), but with so many around him leaving, the series can no longer function. Without them, there’s no other choice but to bringSex Educationto an end.

Ola (Patricia Allison) and Lily (Tanya Reynolds) on ‘Sex Education’

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Season 4 of ‘Sex Education’ Is Going to Badly Miss Lily and Ola

Perhaps the most interesting character inSex Educationis Lily (Tanya Reynolds). She entered Otis' life at school as the extremely awkward girl obsessed with the idea of sex (especially alien sex) and losing her virginity. Otis has his own sex issues, which are bound to happen when your mother has made a career of being a sex therapist. They decide to be each other’s first, but of course, it goes horribly wrong. Otis then moves on to the new girl, Ola (Patricia Allison). She falls hard for Otis, though he completely blows it due to his complete infatuation with bad girl Maeve (Emma Mackey). In one of the best twists of the series, Lily and Ola fall in love with each other. They have their issues, but they are also the healthiest couple onSex Education. The two only want to take care of and be better for the other. Throughout Season 3, their story took up more and more screen time.

Then a strange thing happened. Last July, Netflix announced that they were not bringing back Ola and Lily for Season 4. What?!As Reynolds told the Radio Times, “It’s just the natural progression of these shows — when you have such big ensemble casts and so many characters, I think you have to let a few older characters go to make way for newer ones, which is absolutely the right thing, the way it should happen.”

Maeve (Emma Mackey) and Eric (Ncuti Gatwa) on ‘Sex Education’

Reynolds may have given the polite, safe answer, but the decision makes no sense whatsoever.Ola and Lily had become the best-written part ofSex Education. They were not only the healthiest couple, but pretty much the only lesbian one. Yes, the series does have a big cast. It takes place in a high school. You can’t do that without having the focal point on students, their parents, and teachers. Getting rid of two characters, especially two as popular as Ola and Lily, doesn’t solve a problem. It only creates one. Why do we need new characters introduced when the current ones are thriving? Just with that news alone, the signal seemed to be thatSex Educationcouldn’t go on much longer.

Two More ‘Sex Education’ Stars Are Moving on to Other Projects

Otis' two best friends inSex Educationare Maeve and Eric (Ncuti Gatwa). Watching their growth, through and outside their relationship with Otis, has been what the series is all about: teenagers growing up and changing. Otis starts a sex therapy business at his school, with Maeve finding him clients. Through that, they find each other. Otis is crazy about her beauty and free spirit, and Maeve, a girl with a drug-addicted mother and a little sister she has to raise at times, is drawn to this boy who looks at her and sees the person underneath the hard exterior. Then there’s Eric. He’s easily the most charismatic character onSex Education. Eric is loud and confident and loves to laugh. He’s gay, everyone knows that, and he doesn’t care. He wants to be who he is. But when he gets beat up by a bully because of his sexuality, Eric begins to question everything. Confidence wanes, replaced by a quiet boy who retreats from himself. The journey of watching him rediscover himself has been a joy to watch.

Now, they too are both leavingSex Education. There’s at least a good reason for it. Emma Mackey, who plays Maeve,told Radio Times back in Februarythat Season 4 would be her last, adding, “I’m not in it as consistently.” Her career is beginning to take off without the series. She was one of the final three choices to be Lois Lane forJames Gunn’sSuperman: Legacy. Even more impressive is the man behind Eric, and the reason why he too had to leaveSex Educationafter the fourth season. Why, you ask? He was cast as the next Doctor inDoctor Who! In February,Gatwa took to Instagramto say, “Last day. Last time. Bye bubs, thank you for all the lessons and for all the strength."

Otis (Asa Butterfield) and Jean (Gillian Anderson) in ‘Sex Education’

‘Sex Education’ Has Always Been About More Than Otis and His Mom

The earliest episodes ofSex Educationfocused mostly on the coming-of-age of Otis and his interactions with his sex therapist mother, Dr. Jean Milburn. It made for some great awkward comedy, but there were also just so many times an audience could watch Otis being embarrassed by his mother. Everyone had to grow. Otis goes from a scared virgin into a teen obsessed with sex. Jean grew too, finding a man in Ola’s dad, Jakob (Mikael Persbrandt), anddealing with the surprise of becoming pregnant in her fifties. To add to the drama, Jakob isn’t the father.

None of this growth happens without the people around Otis. He doesn’t become who he is without Maeve, Eric, Ola, and Lily. These are the four people who have shaped who he is the most. They’re not just side characters. TheyareSex Education. They can’t be replaced with different cast members. Season 4 without Ola and Lily is already going to be strange enough. The series can’t last without Maeve and Eric there too. Is Otis supposed to just hang out by himself? Does he suddenly hang out with an entirely new group of people because somehow everyone he knows is moving away? That’s not plausible.

Even if everyone was coming back, Season 4 is probably still the best place to endSex Education. We will have followed these teenagers for four years. How many more stories can be told? It’s time to let them go, let them love and lose, let them get laid, and let them live without us watching.

The fourth and final season ofSex Educationpremieres September 21 on Netflix.