I feel like Ren and Martyn miss their Dogwarts days in different ways because it’s like… Ren missed what it was. Being king. Having a loyal right hand man. Having an army. Protecting his friends. Building a strong fortress. Having a purpose to fight for.
It’s like how Ren was so sad in his first days in Last Life because he was all alone, then went and dramatically declared his loyalty to the Fairy Queen Lizzie not unlike how Martyn declared his loyalty in Third Life. With the Fairy Fort, he had a faction to fight for, a queen to protect. He felt like he belonged somewhere. He liked building his watchtower, liked making the secret basement, liked organising meetings with his faction. He may not be King anymore, but he’s still furiously protecting his friends.
Then came Double Life. Ren was ecstatic that his soulbound was BigB (“best friends forever, baby!”) because they could belong to each other. Ren set up an intimidating fortress (“Box”) to protect them, not unlike Dogwarts’ walls. He desperately wanted things to work with BigB (even though he found a secret soulmate in Martyn), and even did marriage therapy with him. They were loyal to each other. Ren very much liked the idea of people being loyal to each other. Of course, he ended up tangled up with Martyn in every life anyway, because he provided him with what Ren liked. Loyalty, theatrics, and trust.
But Martyn? Martyn missed who it was.
Even in the Southernlands, Martyn always kept an eye out for Ren. He gave Ren netherwart, put out his fire, and for what? In Double Life, Martyn did kind of try to be allies with his soulbound, but he wasn’t very good at it. Martyn didn’t miss being loyal to a partner. He missed Ren. And while Mean Gills was more functional than DL Martyn and Cleo, Martyn still backstabbed (a willing) Scott in the end. And spent his entire red life with the Red Winter scarf around him. And monologued about being an unguided hand, how he cried so hard when Ren died it shattered his soul, and his last thoughts before he died was literally Ren at the altar.
So maybe Ren never left Dogwarts as a faction, an organisation, and home. But it was Martyn who truly never left Ren’s side. Ren missed having a home. Martyn missed Ren, because Ren was home.