There seems to be a lot going on here, I'll just write down some of my thoughts, hopefully you will find some of them useful.
- Being gay can be very hard, I won't deny that. But it's important to keep in mind that what makes gay life so hard are all the bigots out there. Being gay, per so, is not a problem; bigotry is. This may seem like an academic distinction - after all, a hard life is a hard life, right? - but I think it would be an important shift in perspective for you. Yes, you may be facing hardship because of your sexuality,
but there is nothing wrong with you. It's a cliché, but it's true: learn to love yourself, as you are. You will find a world of other LGBT folks who've also accepted themselves and are here to embrace and support you.
- I don't see pornography per se as a problem either, but I will say that it can be very hard to deal with porn if you're prone to mental problems like depression or anxiety (and it seems you are). I know that because I've had problems with this myself. This is what's currently working out for me: I made this rule for myself that I'm not allowed to use tumblr (which is my main source of porn) before 17:00. So far I've had the self-discipline to maintain that rule, and it's really helped. Maybe you can make your own rule regarding porn. Make sure to only make rules for yourself that you know are realistic; nothing is more demoralizing than making a rule and then breaking it.
- On your buttplug-adventure and fear of STD's: just inform yourself, man. And recognize that those disasters and anxieties are expressions of your troubled mind. Pull yourself together mental health wise (easier said than done, I know), and those "problems" will turn out to be no problems at all.
- On being attracted to your cousin: Perhaps your attraction is a way for your currently anxious and troubled mind to express itself. Sometimes, if we are troubled, we tend to seek out inappropriate objects of attraction - be it a straight and therefore unavailable friend, an abusive man, or in your case, somebody underage. The fact that you're also attracted to men your own age seems to point in that direction. I would try to not obsess over it as far as that's possible, and focus on the sexual feelings you have towards men your own age and older.
- That being said, it's also possible that you have pedophile urges.
Here is a podcast that discusses this subject in a way that I thought was very empathic, kind, and reasonable. You can start listening at 10:50 (there is lot's of other stuff before). They also discuss very practical options, and what people who have such urges should and shouldn't do, including the legal aspect of the issue.
http://www.savagelovecast.com/episodes/183
- Overall, I think you sound very troubled, and I'd urge you to seek professional help. I really, really mean that. I hope I could help and wish you all the best!