Rehabs do not cure addiction. Best case, a rehab can teach a highly motivated guest some of the tools of recovery. The real hard part begins after rehab. Generally speaking, it's usually better for everyone, when a former rehab guest tranisitions into a sober living enviornment instead of returning home.
Where's home for this guy?
There is nothing you can do or not do that is going to keep him clean or cause him to relapse. You are not that powerful. None of us are.
Consider taking the time to figure out your own boundaries for this or any relationship. A boundary begins with " I will/will not..." Examples of boundaries include:
I will not be in a relationship with a liar.
I will not be in a relationship with someone who steals.
I will not be in a relationship with a criminal.
I will not be in a relationship with a drug addict.
A boundary is your bottom line. We are responsible for enforcing our own boundaries on ourself. If/when we find ourselves in a situation that challenges our boundary, we take responsibility for ourselves and remove ourself from the situation.
Many confuse boundaries with attempts to control other people. Most attempts to control someone else begin with " You will/ will not...or else..." We have no control over other people. The more we try to control other people's behaviors, the less time we spend controlling ourself and our own reactions. And that's the only thing we do control.
There's absolutely nothing wrong with taking a break from this relationship and figure out what's important to you.