相手・to care・漢字とひらがな・'finally'

I was wondering about some select things.

相手
I frequently play video games with my friend in Japan. We play online, and have other teammates. The word 相手 happens frequently. I assumed it meant teammate. However, sometimes my friend uses the word in a way which suggests that it means opponent, too. Does it carry double meaning and therefore simply could mean 'other player', either good or bad?
Sometimes, 相手が弱かった, '[Our] aite were weak', and then 相手倒せなかった 'I couldn't defeat aite'.

To Care
I was wondering how to say 'I care about ~' or 'I don't care'. For I don't care, I'm guessing there's a few ways to go about it. My guesses for that are べつにいい or 関係ない (the second is more of a guess floating in my brain).

Kanji Reading
Is there any major difference in tone to a Japanese person if I say, お休み over おやすみ? Any nuance at all that comes across if I use kanji over hiragana?

'Finally'
やっと、ついに
Wondering how to express 'finally' in the sense of 'it finally happened!' 'we finally won!' etc. I'm only familiar with yatto and tsui ni but don't know of any nuances between them...

1. 相手 = Typically (although not exclusively) refers to opponent. In other words, the meaning of enemy isn't hard-coded into the word 相手, but in sports and games that is usually that is how it is used. There could be certain contexts in multi-player games where 相手 refers to your own teammates, but this would be clear from the situation.

2. Other options for "I don't care" might be: 気にしない (Pay no mind - can be used to indicate that you yourself are not paying any mind to something, or can be used to invite your listener to not worry about something, as in 気にしないで).
Or どうでもいい ("who cares about that?" "I couldn't care less"). どうでもいい is dismissive and curt. Fine if that is your intention, but you do not want to cause unintentional offensive by using it in the wrong situation. Maybe get a feel for its use by hearing how other people use it before jumping in.

3. Not really. In short phrases (like おやすみ) it is common to render it entirely in hiragana. However, it is equally as common to use kanji, as you have done. Maybe hiragana is a bit "softer", slightly more casual. Also good to remember that too much hiragana strung together starts to become confusing.

4. Finally = in addition to the two you have, you could also use ようやく. This might help
「やっと」、「ようやく」、「ついに」などの違いは? - 日本語を... - Yahoo!知恵袋
(although I read it and was slightly confused by it )

Consider:

結婚相手
話し相手
遊び相手

It just refers to the other guy(s) involved in what is going on. Whether that is adversarial or not is going to depend on the situation.

For "I don't care", it can vary by what you meant by that phrase in English. It doesn't always carry the same connotation.

Example:

A. John is dating Sally.
B. I don't care.

A. Is it alright if I use your phone?
B. I don't care.

やっと also can mean "barely".
e.g.
やっと勝てた。（＝どうにか勝てた。）
We could barely win.

Hey, ledojaeger,

I don't care...many, many ways to get this message across.

どうでもいい - more along the lines of how kids today use "whatevs." A truly "I don't care" attitude.

別に - more along the lines of "I have no special attachment or feeling about it." This can imply an ending that isn't included specifically in the sentence (e.g. 別に、かまわないけど or 別に、いいじゃないですか。)

関係ない - this was another one of your candidates...I don't think this has as strong of a "whatever" or "I don't care" connotation. More like, "it doesn't matter" or "it's/that's irrelevant." Maybe just a different nuance by degrees.

かまわない (or かまいません) - this one didn't come up, yet, but it's a good one. From the verb 構う・かまう, which means to care, to be concerned with, etc. You've probably heard this a million times with or without realizing it...generally as "I don't care/fine/ok/I don't mind" in response to a question, or (a bit more rare in real life, but you'll hear on anime and TV dramas) 構うな! (BIII + na) = Leave it! Don't concern yourself with it!

Wow, everyone, thank you so much for your help!
I'm sorry I'm late on the draw to respond and thank you all. I run around a lot in my daily life, work a lot, and force myself to study Japanese (as I'm not yet in college courses for it, I go through textbooks on my own time, but have to really keep at it and be good about studying even when I'm busy). So, sometimes I post questions and am not able to give a comprehensive answer until later, but I am seeing them all and appreciating them all.

Majestic,
Right, I get that 'curt' feel when I hear どうでもいい, so using it myself would have to be very contextual. I'd rather have a firm grasp on は and が before I sling around どうでもいい, haha. Thanks for your advice on kanji/hiragana. As for me, I LOVE kanji as a writing system, couldn't imagine just using hiragana. There are my students who loathe kanji but I find them a joy. Your explanation of 相手 made a lot of sense to me. Thanks for that link, too. In English we have a lot of expressions for that... 'Finally!' 'At last!' Although 'At last' I generally find a bit dramatic.

Toritoribe,
I never knew that about やっと, that's good to know. Is it barely in the sense that we use it, maybe like... やっと間に合った We just barely made it?

Mike Cash,
That explanation of 相手 also really helped. So it really is contextual and doesn't necessarily firmly mean opponent or ally alone. And this is also true, that if someone asked me their opinion of something, 'I don't care' could be very mean, but if someone stresses over my thoughts about something, a gentle 'I don't care' could be a nice response. I don't know. Language is never quite clear-cut perfectly.

Butarox,
You're so right, I HAVE heard it so many times, and was even just wondering about it mildly when you connected the dots for me! So it's 構う, is it. I've heard 構いません frequently. Is it polite to use?

ledojaeger said:

I never knew that about やっと, that's good to know. Is it barely in the sense that we use it, maybe like... やっと間に合った We just barely made it?

Click to expand...

Yeah, that's right.

ledojaeger said:

You're so right, I HAVE heard it so many times, and was even just wondering about it mildly when you connected the dots for me! So it's 構う, is it. I've heard 構いません frequently. Is it polite to use?

Click to expand...

Yep. Just like any verb...can be used politely, familiarly, or impolitely.

Person 1: これ、使っていいですか？(can i use this? do you mind if i use this?)
Person 2: あ、かまいません (yeah, no problem/sure)

Of course, there are a million variations (ok, not literally a million, but a lot) that Person 2 can use in this situation.

Ex.
どうぞ。
いいよ。
使っていいよ。
うん。(that sound you make in your nasal passage to signal yes)
Etc.