Every soldier carries things important to them. Liutenent Jimmy Cross for example, carries two photographs of Martha as well as her letters
Just as Lee Strunk makes it out the tunnel alive, Ted Lavender gets shot. Cross blames himself because Martha had his undivided attention even during a situation like this.
They joke about Lavender to cover up how much they actually care.In the end, they do feel remorse, however they are just glad to be alive. Meanwhile, Cross continues to hate himself while developing hate for Martha.