@Champaganesupernova
Your DSS needs help and if you allow him to come and live with you this isn't help, this would be enabling him.
You can set all the boundaries/rules that you think will help but what happens when/if he breaks them. It will be so much harder to get him to leave than to say No now.
He sounds like he is addicted to gaming. To help him, you and your DH need to take a big step back. Get on with your lives and look after yourselves and each other. This may help.
I am an addict. I need your help.
Don't lecture, blame or scold me. You wouldn't be angry with me for having cancer or diabetes. Addiction is a disease, too.
Don't let me provoke your anger. If you attack me verbally or physically, you will only confirm my bad opinion about myself. I hate myself enough already.
Don't let your love and anxiety for me lead you into doing what I ought to do for myself. If you assume my responsibilities, you make my failure to assume them permanent. My sense of guilt will be increased, and you will feel resentful.
Don't accept my promises. I'll promise anything to get off the hook. But the nature of my illness prevents me from keeping my promises, even though I mean them at the time.
Don't make empty threats. Once you have made a decision, stick to it.
Don't believe everything I tell you; it may be a lie. Denial of reality is a symptom of my illness. Moreover, I'm likely to lose respect for those I can fool too easily.
Don't let me take advantage of you or exploit you in any way. Love cannot exist for long without the dimension of justice.
Don't cover up for me or try in any way to spare me the consequences of my addiction. Don't lie for me, pay my bills, or meet my obligations. It may avert or reduce the very crisis that would prompt me to seek help. I can continue to deny that I have a problem as long as you provide an automatic escape for the consequences.
Above all, do learn all you can about addiction and your role in relation to me.
I love you.
Your Alcoholic