Caught in a love triangle. HELP, please?

I have a boyfriend, his name is Shane. And he has a best friend, his name is Dylan. Dylan and Shane have been best friends since they were little kids running around the streets of San Juan, Puerto Rico. Me and Shane have been together for a year, as of today. Today's our one year anniversary. Before me, he's never been in a relationship longer than 4 or 5 months. We both love each other more than anything in the world, anything. I've been there for Shane, through everything. He lives such a hard life, it makes me wonder how he's even still alive. In the past year, he's had to deal with an involuntary heroin addiction (his dad being the sick bastard he is, injects the heroin into his arm. That addiction has lasted for 3 years), abuse from his mom and dad, his mom passing away the day before Christmas Eve, and his little sister dying three weeks later. His grandma passing away in April, his brother overdosed and passed away in May. Almost dying from the abuse. His dad raping him, his little sister, his other best friend, his mom, his dad's SISTER, step-mom, and step-sister. His dad breaking one of Shane's ribs, the same wrist twice, over 20 hospital trips in one year, an alcohol addiction, smoking for three years, diabetes, heart problems, and to top it off, he's dying. He has some sort of life threatening problem, that no doctor knows what it is. He won't make it to 25. He's almost 19. Anyways, that's not even half of what he's had to deal with. I said all that because I've helped him through ALL of that, we're closer than ever before. But. Dylan has had a past of liking Shane's ex-girlfriends, she likes him back, leaves Shane and he ends up alone. Apparently that's happened more than once. But I just recently found out, that Dylan has feelings for me. And it's more than just 'liking' someone, he said he's falling in love with me. Which honestly surprised me, 'cause me and him have been close friends for a while. But once he said that, I started to realize that I have feelings for him, maybe more feelings than I should have. Just last night, Shane found out that me and Dylan have feelings for each other. And he was devastated, absolutely hurt. It sucks 'cause today is our one year. I knew something like this would happen on a big day like today. What in the WORLD do I do? I honestly think, these feelings won't go away for Dylan. Then again, I'm head-over-heels in love with Shane, and I forever will be. I just don't know what to do. Some people are telling me to stop contact with Dylan, others say leave Shane to be with Dylan. I'm so confused. Help. :(