First, please do not believe your thoughts specially if they are so destructive and if they make you feel crying and completely unable to maintain your usual daily activities.  There is a good technique which helps to combat such thoughts, where you try to distance yourself from them and just find a mental spot where you can observe them and you will very soon realize they are not you. Maintain this position as long as you can. ˝I am not my thoughts, I am thinker of the thoughts, but I am not my thoughts. They have no power over me. No descending into them. I am free.˝ Feel this with both your heart and mind and you will be soon free of them and have a clearer picture.

Second, I urge you to stop watching pornography, because it is highly destructive to the psyche, specially at young age such is yours. Porn is very suggestible because it relies on basic human need / instinct of sexual drive, but it completely distorts it. It counts on body instincts alone.  Since we are visual beings, those images literally go into our consciousness and get life of their own which overburdens the psyche.  The psyche instinctively knows pornography leads mental health downward and that it distorts true purpose of sex (emotional attunement and loving union of body, mind and emotions which leads to most beautiful climax.)
Please, cut it out and whenever you feel the urge to watch it, try to channel that urge into something creative.  But you need to realize this for yourself.

Hope this helps.