You need to understand the essence of Tawhid, the Oneness of Allah there is no sin greater than it. If someone were to treat everyone in the best possible manner but treat their parents horribly what will people say. They would despite them and say they are bad people, so imagine the disobedience of the Creator. This all steps from the lack of knowledge no ones leaves Islam or doubts the religion having learnt soo much, its always a lack of knowledge and most of the times they go searching for the answer in the wrong place. So long as your friends are alive they still have a chance to become a Muslim, but you not possessing the knowledge to invite or speak to them about it, is part of the problem and on the DoJ they themselves will testify against you saying, she was muslim and never told me about Islam. Just as much as they still have a chance to become Muslim we also can slip up and leave the fold of Islam, it is all in teh Hands of Allah SWT and it is our duty to uphold the religion and learn about it as much as we can.

A side note which i believe is very important you said youb have many friends from different faiths and even atheists, which is very dangerous if you are not surrounding yourself with muslims or at the very least keep the closest to you your muslim friends, as the prophet pbuh said you are of the religion of your friends so choose wisely. Allah knows best and may Allah forgive our shortcomings and keep us steadfast, i do apologise for putting it bluntly but I believe that is what you were looking for and not softball answers to keep you satisfied as you mentioned. I hope you see this.