Persistent loss streak, and drop in MMR after failing my promo to Gold

Here is the story:

1. I recently got from S3 to S1 and then to my promo to Gold.
2. I won 2/5 games and lost my final one to a fed Katarina.
3. After this, I was like - OK one more game and I will be back in promos.
4. Then I lost 2...
5. From then on, I was just losing like 4 games, and winning only 2
6. Before I knew it, my MMR from Gold 3 (1500) dropped to S3 (disgusting) !!! (according to op.gg)
7. My teams got worse - mainly attitude-wise: Easily tilted, rage-quitting and eventually feeding.

Now, I got demoted to S2 and this is not getting better..

I do not understand what I am doing wrong. I was playing my best champion, and my best role all along until I was demoted to Silver 2.

I play ADC - Jinx, and people very often say that I am really good, or call me a god jinx ( not trying to be a show off, but I want to make sure u know I am genuinely good with this champion - have about 200 games with her and 67% win-rate in total .. or had until now..)

The way I play is:

1. I try to poke with Q/zap, and test the ground to find out if I can get an early kill
2. My main priority is to farm 1300 gold to get B.F. and go back.
3. If I get the turret, I will then go to mid - try to kill the mid-lane and push their turret, and lastly get top - all this to make sure my team is not behind.
4. In the meantime I will make sure we get drakes, or steal them with my R.
5. My core items are: boots, IE, Hurricane, Static Shiv, last whisper, and a situational defensive item (e.g. mercurial/GA)
6. After I have these 3 items: IE, Hurricane, Static - I can easily do tons of damage in a team-fight.

I believe that I do everything I can in all games, I have a very strategic approach to how I play not only my champion, but the objective focused part of the game. I often feel that because one lane is neglected by the jungler, this person ends up feeding both the laner and the enemy jungle - making it easier to then come to my lane as they are ahead.

Sometimes I feel I should play jungle to make sure no lane loses, but in reality this is so difficult! People in this ELO make silly mistakes, go in when they clearly cant fight, or simply don't ward. Before you know it, as you are trying to help one lane, the other one dies.. The way I know I dont make many mistakes like this is that my turret is always the last one to be taken down during a bad game, and this usually involves about 4-5 people diving me and my supp to achieve this.

Please someone let me know how to break this cycle. I have taken breaks from league, but I come back to this exact same reality. That my teammates are impossible to carry!

It almost feels like because I failed my promos, RIOT marked my account as one that is meant to be losing now. Like, I feel like I have absolutely no control over whether I lose or not, that everything is decided by some ancient spirit or just my team...

Sometimes when I am not doing so great winning games, I pick a DUO with someone that is on a win streak. This in most cases seems to solve the problem temporarily. Today I went for duo with someone of higher MMR than me, but also on a loss streak and .. you can guess it. Nothing changed.

I appreciate any suggestions and constructive criticism, but please do take this discussion seriously - I am genuinely trying to find a way to improve..

Thank you.

P.S. Please ignore my Summoner name as this is my very old account!