Its great to see that you are no longer lurking and actively questioning.
you are very mature for your age and its a shame that you had no one who could answer the deeper, more philosophical questions for you.
Don't write off Islam completely, for it will forever remain a rich resource for you. you are fluent in its language, its customs, its followers. Ignore the Muslim teenage angst filled sentimental contingent of TSR, with their condescending tests and what-nots.
There are efforts underway throughout the Muslim world, working together to achieve reform of the Shari'a.
historically the owning slaves and concubines was perfectly legal under the shari'a as inherited from the classical period, but the vast majority of Muslims no longer recognise these practices as morally allowable in Islam. These practices that are supported by sharia rulings have been quietly abandoned in favour of a more bourgeois conception of marriage and family.
Another example is the the presence of eunuchs. Castrated formerly male servants were once ubiquitous in aristocratic Islamic homes , royal courts, and even at the Prophet's tomb in Medina. Rulings about these "males made non-men" are found in the shari'a, but most contemporary Muslims are horrified by the idea of castration and the resulting gender ambivalence.
....yet another example is the gender equality between men and women. This is increasingly accepted by Muslims in the work place and home, despite the fact that the marriage contract inscribes highly differentiated rights and privileges for men and women... many contemporary Muslim women are shocked to discover the real nature of their marriage in shari'a terms and its underlying legal rationale as a contract of sale.
I am a gay Muslim. If anyone had a reason to leave Islam it would have been myself.
I am not asking you why you have left Islam. I respect your decision. When intelligent people don't get the answers they need, they are going to get frustrated and leave.
Times are changing. Be a part of that change.
I am here for you. Whenever you need me.