A part of me died on July 28th, 2014.

My best friend, my boyfriend, and my partner in crime passed away in the early morning, just hours after I spoke to him. His killer was silent and deadly. This enemy had taken control of him months before he died.

Heroin. It’s not just my enemy – the thing that stole someone I truly loved – but, strangely, it is also something I have become obsessed with learning more about.

Heroin’s addictive power began taking over my friend in December 2013 and continued eating away at him until his death just eight months later. He kept his secret hidden for months. I failed to realize this was possible with heroin because I didn’t understand it could be taken in other ways besides injection. Smoking or snorting heroin is a psychologically easier way for a teen to start using the drug, and is also harder to detect.

Over time, I noticed my friend was moving sluggishly and having trouble understanding simple things. At the time, I didn’t know these were side effects. Others include nausea, vomiting, itching, diarrhea, rashes, sexual dysfunction, bruised or scabbed skin, involuntary kicking, cold flashes, and muscle and bone pain. The senses become dulled too. My friend’s sense of smell was virtually nonexistent. His vision worsened, he could never hear a thing I said, and he wouldn’t notice if someone brushed against him.

There were other signs – not necessarily physical – that I should have noticed. This guy who had always been into fashion had let his appearance and hygiene deteriorate. People constantly commented on the same pair of pants he wore for weeks on end, the bitter smell emanating from his body, and his surprising weight gain.

He personality began to change. He became deceptive and lied constantly. He stole and had angry outbursts. Money became his one passion, because he used it to feed his addiction. He also began acting up in school. He went from being an honor roll student to barely showing up. Instead, he stayed home to drink, got arrested, and did drugs at work. Other behavioral signs that someone is using heroin include deceptive behavior, avoiding eye contact, increased sleep, slurred or incoherent speech, loss of motivation, withdrawal from friends and family, repeatedly stealing money, hostility, and decline in self-esteem.

The fact that I did not recognize these signs in time to save my friend haunts me every day. But that is another mark of a heroin addict; they make sure to keep it hidden from those they are closest to because they know their loved ones will fight the hardest to make them quit.

A heroin user’s journey typically begins with prescription painkillers such as OxyContin, but once that habit becomes too expensive, the addict will turn to other drugs with similar effects. A major contributor to the rise in heroin use in the U.S. is the fact that the drug is dirt cheap. My friend initially said that heroin was just something he was “trying out.” It wasn’t a problem, he claimed. Anytime anyone asked him about it or displayed concern, he was instantly defensive.

Heroin is a particularly dangerous street drug because it is impossible for users to tell how pure or clean the heroin is. Drug dealers often mix it with other harsh chemicals, not only to make it stronger but to sell more of it more cheaply. Street heroin’s lack of purity leads to overdoses and deaths, and the problem is only getting worse; from 2010 to 2012, heroin overdose deaths doubled in the U.S., according to the Centers for Disease Control.

Heroin not only harms addicts, but it has a huge effect on their family and friends. My friend took “bad heroin” or “dirty heroin” the night he died. That night we had a fight and I refused to go see him like I had planned; he was acting crazy and angry, and he wasn’t himself. The last thing he said to me was, “No one will ever love you the way that I love you.”

When I responded to his text the next morning, it was already too late.