Addiction is progressive. He was popping pills. Then snorting. Now shooting IV. What's next?
Opiate addicts often find suboxone useful when they are temporarily unable to score their drug of choice. Those who are serious about getting off the junk, don't buy subs off the streets. Your guy is just doing what addicts do.
None of us would be here if all it took was love and support to get our friends and family off the junk. There is nothing you can do or say that is going to cause him to stop. You are not that powerful. None of us are.
Keep in mind that he is not using dope at you. It's not personal. It just feels that way.
Drugs have rewired his brain to protect and sustain addiction. Lying, stealing and manipulation are the tools of addiction. When you give/loan money to an addict, you are enabling their addiction.
You have the choice to remain front row center to all of this and more, or not.
You can get off this crazy train any time you want to do so, when you are ready to do so.
In the mean time, stop, just stop giving him money, protect your money, credit cards, checkbook, jewelry and other stuff that can be traded or pawned. Double up on birth control because HIV and other nasty stuff are common with IV users. Parethood does not cure addiction. Separate the hopeful fantasy of the guy you need and/or want him to be and focus on the here and now.
I don't know you although I know you deserve a better relationship than being the third wheel to a guy and his dope.