Difference between sin and shirk

Q: How to differentiate between sin and shirk (especially major shirk) Example:

1# If a person does many haram acts because of his desire and continues it without fearing Allah then will it be just a sin or it will be considered as he is following his desire? Is it shirk as mentioned in Quran [45:23] “Have you seen he who has taken as his god his [own] desire, and Allah has sent him astray due to knowledge and has set a seal upon his hearing and his heart and put over his vision a veil?

2# We know interest is haram. If a person continues to take interest after knowing it haram or does not pay zakat, does it mean that he loves money more than Allah and doing shirk as mentioned in hadith “He who became the slave of the Dinar or the Dirham will perish and be destroyed.” [Hadith Bukhari] So are these just sin or they are shirk or they may lead to shirk even major shirk?

Getting married as soon as a suitable match is found

Q: I know a girl for 7 years. In the last 6 months we started developing feelings for each other and dated a few times but nothing physical. We have decided to stop dating so that it does not damage our future together. We plan on getting married in 3 years time. Is it permissable to read istikaarah salaah now even though we plan on getting married later and what is your advice for this period of time?

Gay feelings

Q: I have gay habits in me and I am seeing a Muslim man. I am in my 30s and not married due to home responsibilities as I am taking care of my mum who has no legs and in a wheelchair. It worries me that I have these feeling in me from an early age. Please advise.

Haraam relationship

Q: Today one incident happened when I go through internet I get to no there is thing like if we do something that Allah doesn't like it's shirk so the thought that came to my mind is my friend who is a girl so I thought talking to her is shirk but I search in the internet in that they have told like it is minor shirk so I keep searching until I clear this doubt and then there were some post like it can be major shirk so to be frank I really don't want to do that if its major shirk but I want to make this doubt go dissapear so I kept searching at last I got to no Thera is no prob but now I feel like I was ready to talk even if it is major shirk but to be frank I don't no wat I thought ... it can be true that I might thought or not but am not sure but I was searching whole time to make That thing normal but now it feels like I commuted shirk and here after talking to her is shirk .... so I don't no wat is true what is right and wrong anymore unlike other issue this feel real because I was very clear than other incident that happened bcz of waswaas so now I can't say it's waswaas or me .. and definitely can't say like I was nt ready so what can I do ... I just want to be safe from shirk so is there is any way I can ask forgiveness and talk to hey normally or should I ask forgiveness nd stop talk to her ... u might be mad to hear this but plz hlp to understand.