I do understand your turmoil - I think anyone who is seriously thinking about God has to grapple with things like this re the unfairness of life.
I would say, though, that if you want to hear what God thinks about what you're going through, ask him. Get real with him - tell him you're struggling, that things aren't fair, that if he is who he says he is, why do bad things happen to good people? Tell him the whole kaboodle - rant if you like (he can take it!). It's a good idea to read the bible and ask him to show you what it means - though take it easy, try not to sweat it. also talk to other christians - as you are on here, but RL people too. choose carefully who you talk to, see them in action first.
You are bereaved and it is very hard to think straight when you are bereaved. The pain is immense. You wonder why someone so good and fair was taken in a horrible way. Though bereavement is a legit and achingly human space, one which, as it happens, is very close to God's heart. I have had a very painful life and it is a great comfort to me that God knows all about pain: Jesus is described as a man of sorrows, aquainted with grief.
As for sin - yes, that's a thorny one. The word 'sin' is so heavily laden isn't it? Dripping with guilt and disgustingness. I agree that people bandy the S word around a lot without even attempting to explain what it means. It's all a bit jargony, I find. To me, 'sin' actually means separated from God, not in relationship with God - just a fact. I believe we are born in that state, it is the natural human condition. God's total being is entirely about love, and it is pretty obvious we aren't the same: though we can and do love, we aren't entirely devoted to love, as he is.
imo God isn't shocked that we are separated from him - he kind of knows all about it tbf. There is a wide spectrum of what people do with the state of being separated from God, of not being in relationship with him: some people are good and very good, some are bad and very bad; the majority bumble along in the middle, wanting to generally be decent folk. All of that - good, bad, middling - doesn't win or lose points with God one way or the other - the only thing that is capable of mending the separation with God is Jesus, who literally paid the price to mend the broken relationship; to facilitate a full and proper relationship, not a po-faced, rulesy, fusty, guilty 'relationship' but a love-filled, loving, natural relationship, free and open (nothing hidden).
Which means when you are angry, either with God or life, or confused, hurt, doubting etc, you can say so - to God. It's a relationship he has very clearly stated he wants and has gone to extravagant lengths to facilitate.
imo, wherever you are at - whether doubting, unable or unwilling to accept Jesus as the bridge, you can still be straight with God, chew the cud, bash it out with him; ask him for help, show him your broken and confused heart. Etc. though I would say don't take the piss - but I don't think you're in that space tbh. And I would also say, check it out with the bible: read it and ask God what he means by it (or the bit you're reading - you don't have to read vast chunks).