It's hard to drag myself away from a visual novel... Anyway, here's the stuff that's caught my eye so far. It's a mix of grammar, personal preference, and maybe some misconceptions, but see what looks good to you.

)
5/9:
Old: so I'm assuming he doesn't want to do it with
stragers.
New: so I'm assuming he doesn't want to do it with
strangers.
5/13:
Old: I've done most of what love can do in my
simulation.
New: I've done most of what love can do in my
situation.
5/14:
Old: It seems I picked a
quarrel with you.
New: It seems I picked a
fight with you.
(preference; more common form)
Old: If
you're a happy person
that believes people are naturally attracted to one other if they are together... Or if you held the common belief, thinking that you can't live together unless you love or like each other... You
couldn't understand the relationship between me and Risa.
New: If
you were a happy person
who believed that people are naturally attracted to one other if they are together... Or if you held the common belief, thinking that you can't live together unless you love or like each other... You
wouldn't be able to understand the relationship between me and Risa.
(Tensing is a little awkward here, among other things. This sounds better, at least to me.)
Old: Kotarou probably
knows too.
New: Kotarou probably
knows, too.
Old: just because you've lived
10 more years than I have. You're not the only one who's lonely and can't get what
you want.
New: just because you've lived
ten more years than I have. You're not the only one who's lonely and can't get what
they want.
(10/ten might be preference; "you" doesn't really match up well with the "the only one" that it refers to; does a singular "they" work any better?)
Old: I don't think it'll leave a
scar either...
New: I don't think it'll leave a
scar, either...
Old: You shouldn't go
drink outside.
New: You shouldn't go
drinking outside.
Old: You're probably much more normal than
me or Risa.
New: You're probably much more normal than
I or Risa.
Old: We're both good-for-nothings
that gave up already.
New: We're both good-for-nothings
who have already given up.
Old: And it's painful because I
can't ever obtain them.
New: And it's painful because I
can never obtain them.
(personal preference)
Old: and relatives
that would accept me if I
go over to their houses.
New: and relatives
who would accept me if I
went over to their houses.
Old: We're similar in those regards...
Kotarou too.
New: We're similar in those regards...
Kotarou, too.
Old: Just like how I
would never have a blood-related family or
a relative...
New: Just like how I
will never have a blood-related family or
relative...