When I was in rehab they stressed not getting into a new relationship. They were very supportive of family and wives and girlfriends that were clean themselves and not using drugs. The rehab thinking is for the addict to not get into a new relationship because it takes the focus off them working on themselves and we are as newly clean addicts very friable emotionally. They mainly don't want people getting clean and going back to friends and family that are in active addiction because it's way to tempting and stressful to stay clean when everyone else is messed up and the drugs are lying around. Rehabs don't want to split up supportive relationships that were in existence prior to rehab. If he's telling you this either he doesn't understand what the counselors mean or he's wanting out.
You on the other hand need to find support for yourself in this time, you can't depend on what he will or won't do, you can't make a person be clean unless they want to be clean and sometimes living in a homeless shelter is a consequence the addict needs to decide it's time they get help and get to living a better life. His family may have been through the ringer with him and it doesn't mean they aren't supportive, it could just mean that they realize nothing they say or do will make much difference until he wants recovery truly and for himself. They've wisely allowed him the space to make his own decision as to where his "bottom" is on drugs. I hope the best for you and your child. Save your energy for rest and moving forward with your life regardless of what he does.