You are a horrible person for using that icon, Nadia, just so you know. :|
Joshua adores his brother. Plain and simple. Even if they're not related by blood, and even though he knows they'll be enemies again if he's sent back to their world not to mention the whole "going home probably means losing his memories again" thing, he's still happy that he gets to spend time with his brother again here in Luceti, where he doesn't even have to worry about the society. The circumstances still aren't ideal, sure, but he's pretty content nevertheless.
...The thing is that he may very well be a bit too attached to Leonhardt. For one, it's a major contributing factor to Joshua's increasing complacency in regards to Luceti - knowing what returning home means, especially now that he's aware of Leonhardt's eventual fate there definitely manages to curb his desire to leave Luceti again... and combined with the fact that both of the people he cares about the most are here now, that pretty much means he has little to no incentive to keep trying to find a way to return.
For another, his attachment has arguably hit a point where it borders on being damaging for Joshua. He handles things like Leonhardt getting hurt like he did back during the December draft a lot worse than he would if it were someone other than him (with one obvious exception)... let alone things like him dying, as proven by recent events. Factor in Leonhardt's own tendency to be suicidally overprotective (even if that's getting a bit better now), and... well, it's a bad combination, to say the least. And much like the above, this also feeds into his lack of an incentive to find a way to get back to their world, since that means inevitable death for Leonhardt unless they somehow manage to keep their memories of Luceti, which seems increasingly unlikely at this point.
TL;DR: Joshua still adores his brother, but worries way too much about him as a result and all of that leads to him having practically no desire to go home. And I would not be the least bit surprised if that leads to an argument in the future, like you said. I think I'd be more surprised if it didn't, really.
Spoiler warning for Trails in the Sky!
Joshua adores his brother. Plain and simple. Even if they're not related by blood, and even though he knows they'll be enemies again if he's sent back to their world not to mention the whole "going home probably means losing his memories again" thing, he's still happy that he gets to spend time with his brother again here in Luceti, where he doesn't even have to worry about the society. The circumstances still aren't ideal, sure, but he's pretty content nevertheless.
...The thing is that he may very well be a bit too attached to Leonhardt. For one, it's a major contributing factor to Joshua's increasing complacency in regards to Luceti - knowing what returning home means, especially now that he's aware of Leonhardt's eventual fate there definitely manages to curb his desire to leave Luceti again... and combined with the fact that both of the people he cares about the most are here now, that pretty much means he has little to no incentive to keep trying to find a way to return.
For another, his attachment has arguably hit a point where it borders on being damaging for Joshua. He handles things like Leonhardt getting hurt like he did back during the December draft a lot worse than he would if it were someone other than him (with one obvious exception)... let alone things like him dying, as proven by recent events. Factor in Leonhardt's own tendency to be suicidally overprotective (even if that's getting a bit better now), and... well, it's a bad combination, to say the least. And much like the above, this also feeds into his lack of an incentive to find a way to get back to their world, since that means inevitable death for Leonhardt unless they somehow manage to keep their memories of Luceti, which seems increasingly unlikely at this point.
TL;DR: Joshua still adores his brother, but worries way too much about him as a result and all of that leads to him having practically no desire to go home. And I would not be the least bit surprised if that leads to an argument in the future, like you said.
I think I'd be more surprised if it didn't, really.
... ... ...random icon button, what.