Why doesn't he want him to get him memories back

I think what it is that the MC doesn’t want to pressure him about getting his memories back. Amnesia is a complicated brain injury so his memories could come back in small increments or even not at all or just partially, which would put a high expectation on the ML to recover them and cause him further stress/guilt/angst/depression (he lost both his parents as well and has survivor’s guilt). I’m amazed at how mature the MC is for his age to understand that so quickly. He does in fact really want the ML to recover his memories, but without further trauma.