After Will's death, Jem's first thought had been to come back to London. He could only think of the sadness and pain that Tessa must have felt.
The only thing stopping him back then was his guilt. It would have been like waiting for Will's death all these years to have Tessa back.
And he knew she would have a loving family to support her, as the many friends she had. Through the letters, Jem knew that she and Will kept in touch with the other institute residents over the years. Even the Lightwoods were part of the family after Gabriel married his sister.
So he stayed in the monastery.
However, when he heard London being bombed, his conscience was gone and he just wanted to see her. However, this was not so easy. During the months that England was under fire, he couldn't find a sailor crazy enough to make the months-long voyage through the destructive world. He had considered making the journey overland, but that seemed even less likely.
So he had to wait until things calmed down in England. It wasn't easy after that either, but China and Great Britain were allies, so he was able to make the crossing on a supply ship.
However, the more he saw of Tessa, the more he wished he had left after Will's death.
She seemed to him as lonely as she had been when she arrived in London. All she had by then was her brother, and he just really wasn't someone to rely on.
From last night's conversation, Jem knew that Sophie, Tessa's dearest friend, had died two years after Will. Tessa had had to bury so many longtime friends over the past few years.
The Lightwoods, the Fairchilds, the Blackthorns.
She loved her life with Catarina, but the two didn't talk about personal things.
And knowing her, he couldn't imagine that Tessa would ever tell her children about her troubles. Not out of pride, but because she didn't want to burden them.
So he had no choice but to wait and hope that her later would be in the near future.
They were old, and Jem didn't know if they would have the five years it took Will to tell him his troubles.