"There isn't much sun" sounds fine to me. I wouldn't use it formal writing, but I might say it in casual conversation.

I agree with Eric. Both "me too" and "you too" sound strange in this context. You could say "I want to marry you too."

If you're on a computer, you can find a link to the support page at the very bottom of the screen. (I'm not sure if it's the same on mobile.)

In this context, it means "belittling." To "diminish" something can mean to reduce its (real or perceived) value, importance, dignity, authority, etc.

I agree with Mel. It sounds like it's a huge book, and the writer is making a joke about how it could easily kill an insect.

Your paragraph is well-written and already sounds quite natural. I would suggest deleting the word "but" from "but she is also my unconditional supporter." Normally, when we say "not only X, ... also Y," we either use "but" OR we repeat the subject of the sentence -- not both. For example, we would say either: "He's not only smart, BUT also brave." or "He's not only smart, HE'S also brave." It sounds a bit unnatural to say "He's not only smart, BUT HE'S also brave." Everything else looks good! The last sentence is perhaps a little strange because it says she's "warm and sweet, like a river." Rivers aren't usually described as "warm" or "sweet," so the comparison seems a bit confusing. The grammar is fine, though. :)

It would be fine to say "it" in this case, but the speaker probably said "this" because there is (possibly) more than one hat. The speaker is making a contrast between "this" hat (Amy's hat) and some other hat (the one that belongs to the person who asked if this was their hat). "THIS is Amy's hat. The OTHER hat is your hat."

In many cases they're interchangeable, but if you say you watched someone "do" something, it often means you watched the whole process from beginning to end (you watched the person do the action and complete it). If you watched them "doing" something, you watched them *while* they were doing the thing, but you didn't necessarily watch them the whole time. "I watched him walk up the stairs." -- The sentence implies that he walked all the way to the top of the stairs, and I watched him the whole time. "I watched him walking up the stairs." -- I was watching for at least part of the time while he was walking up the stairs.