Gustave was there for his sister as he promised. Every time someone said as much as one unkind word to her, he was there to defend her. After all, he had four years to make up for.
Twos years later, Gustave was twenty and Catherine was six.
Gustave had wished that he didn't waste so much time with Celeste. Especially since, after all they had been through, he was just tossed aside like yesterday's garbage.
Despite the wrong Celeste had done Gustave, he was still great friends with Lucas. The two spent time together regularly.
Gustave made sure that nothing got in the way of his spending time with his sister, though, as she was most important to him.
As for Erik and Christine, they had talked of having more children, but all they did was talk. The decision they came to was to not have any more children. They wanted more, but decided that it wasn't worth the risk of having another deformed child. One was enough.
It had pained Erik every time his daughter came home in tears from getting picked on. Though, those tears were soon dried once she found out that Gustave had played some cruel trick on his sister's tormentors.
One day, Gustave had just finished his normal act of playing a little prank on the children that made fun of his sister when Lucas burst in, his face red from tears.

"Lucas, what's wrong?" Gustave asked worriedly.

"She's gone. She's really gone. Gustave, my baby sister," Lucas sobbed.

"Do you mean Celeste? What's happened to her?"

"She's...she's dead. Celeste's dead, Gustave."

"What happened?" Gustave asked, choking back tears of his own.

"Henri and Celeste were on their way back here when the ship they were on crashed into another ship. Celeste fell and hit her head. She died soon after," Lucas explained through his sobs.

"And what of Henri?"

"He drowned. The impact threw him overboard."

"Lucas, I'm so sorry. Despite everything, I still did love Celeste. She will be missed," Gustave said, tearing up.

"Gustave, she wrote you a letter. It was found on the inside of her coat pocket," Lucas said, extending the envelope to his friend.

Gustave took the letter and embraced his friend. He felt truly sorry for Lucas.
Lucas was now completely alone. His parents died long ago, leaving him and Celeste alone. With Celeste gone, he had no one.
Gustave talked with his friend for a little while longer before returning home.
As Gustave read the letter, tears stung his eyes. The letter read as follows:

Dear Gustave,

I hardly know where to begin. Let me just start off by saying that I never should have left you. These past two years have been miserable. I married Henri and we have a daughter now. She is a year old. Her name is Christine. I named her after your mother, because after my own mother died, Christine was the closest thing I had to a mother. Gustave, I still love you dearly. I have a plan. I'm going to take my daughter and leave with her in the middle of the night. I'll take off for Paris and we can be together. That is, if you want take me back. Please, Gustave, say you'll take me back. You are the only man I've ever truly loved. Please. My life has been just horrible without you. I need you, Gustave.

Love,
Celeste

P.S. I love you.

"Hey, Gustave, Do you-" Catherine paused. "Why are you crying?"

"Celeste's dead. Before she died, she wrote me this letter. She still loved me. After all these years, she still loved me. Now she's dead and I'll never get to see her again," Gustave sobbed.

Catherine read the letter. "Wow. She had a child with that guy?" Catherine asked in disbelief.

"Wait. Where does it say that?"

"Right here."

"What happened to the child? Did she die too? Does Lucas know about her?" Gustave questioned. "I have to go talk to Lucas."