Do you think that a good muslim who has premarital sex is commiting a grave sin. Do you think a muslim women who does not where the hijab and reveals her ankles or anything below her collar bone is commiting a grave sin?
Going against one part of the Quran yet following its main principles and being a moral and ethical individual will make you a much better Muslim than someone who acts like a strict muslim but instead acts arrogantly, is rude to others, judges others actions without knowing the whole story, does not condemn and acts ignorant towards actions in their own social group.
Do you think owning a slave is fine? Do you think a daughter receiving less inheritance than a son is fair? The Quran allows slavery and supports unfair inheritance against women, does that mean it is still right in this day and age?
Do not approach religion and the Quran in such binaric way of moral duty vs grievous sin for surely God will not and instead judge you on your contributions towards the people of this Earth. In Christianity there is an idea of how we are all sinners and though in Islam there is no concept of original sin, you should know that in the current world nearly all muslims you meet have committed 'sins'. Many would have lied to their parents, not show genuine respect for a teacher, recite the Quran robotically rather than with the heart or had premarital sex, oppressed women (subconsciously [discourage their daughter from doing a specific job and instead tell them to start a family] or consciously).
My teachers always say that the greatest gift God has given us is not the Quran or the Prophet pbuh but instead is the intellect that we have. If you are suffering so much from having gay thoughts and feel that self-mutilation is the only answer then you are not using your intellect correctly. Do what makes you happy, help yourself achieve happiness first and foremost and then help others. All the instructions in the Quran are not there to inflate Allah's ego, he does not want us to pray 5 times a day because he likes people to pray to us, he does not want us to do Hajj because he likes people following his instructions. All of the instructions in the Quran are there to allow us to make our own lives and the lives around us more fulfilling. If you are happier being gay then be gay. No one is made worse off by you being gay and you and your eventual partner in the future will be better of. (do not conflate this with do drugs as it makes no one worse off and makes you better off: drugs cause addiction, social isolation, financial distress and general health issues in the long run)
By you messaging on TSR you've already made the first step by not repressing it and to anyone reading this that is never the solution. Be good to yourself as you are God's greatest creation and you're happiness and fulfillment is definitely more important than arbitrary instructions.
Also, do some critical reading of religion and Islam. I'm sure you've read the Quran already and many hadiths but it is important to understand and acknowledge the intellectual arguments of both sides and remaining in a religous echo chamber is bad for your intellect.