I'd say your family and friends are correct.  And, if dad was once an addict too, one of the worst things for a recovering addict is to be around another user  I'm afraid you got in the middle of a big ol' mess, and now there are tons of pressure for you to fix it.  It is not uncommon, by the way, for SMs to ever be put in this type of situation--they are expected to fix a broken family.  Which, maybe wouldn't be bad if a) it were possible and b) they'd get some recognition for it.  But, usually what winds up happening is SM is reminded of "her" failure over and over to make the family work, and her big thanks winds up being a big wampum a$$-whupping.

When an addict is around, they have a tendency to bring everyone around them down to their level.  If his own father won't deal with the situation properly, how can you be expected to?  Yes, love yourself more.  Don't add another victim, yourself, to this pile of horrors.

I am very against adult sons or daughters being allowed to live in their parents' house, much worse if they are making zero financial or practical contribution to the household, and worse still if they are enabled in their addiction by a parent.   But the cherry on the cake is that your partner allows his son to be disrespectful to you.  This alone would make me want to leave. 

Your fiance is still enabling his drug addicted son, which means he still has not healed his own issues with codependency. Many addicts (like him) end up in codependent relationships with another addict - it becomes their new addiction. Now he's addicted to his son and helping him get well, but he can't help his adult (not "almost adult") son if his son doesn't want to help himself.  Allowing him to live there rent and responsibility free and use drugs while in rehab is enabling and the opposite of helping him.  Much as the son won't change without wanting to, neither will your fiance.

I'd suggest you go to Al-Anon or Nar-Anon because you too are now in a codependent relationship with both of them. It might help you get some clarity on what you have control over in this situation.

There is no win for you in this situation. You need to get your own place. Break up with him and chalk this up to one of life's lessons. I would make this move quickly before you get sucked into their dysfunction further. 

My SS is an addict. Clean now about five years.

After his first in-patient rehab, the counselor advised that SS not move back in with family. He had to learn to live as an adult on his own, and being put back into the same environment would likely lead to the same behavior. But, oh, no, nobody knows SS better than DH and DH insisted that SS would not thrive in the group home, working a minimum wage job, without family "support." That counselor was right of course. SS started using again.

After his second in-patient rehab, SS took control of his life and moved into a group home, attended meetings, worked the program, found a job. SS himself realized that DH was an enabler so cut off DH for a time until SS could reestablish a healthy relationship. I give SS a whole lot of credit for how he took care of himself.

But you can't force your DH or your SS to get out of their dysfunctional, codependent relationship. All you can do is take care of yourself. Would your DH consider seeing a counselor who specializes in addiction issues? That might be your only hope for breaking the cycle.

THere is no shame in taking care of yourself and leaving dysfunction and addiction behind. Do what you need to do to be happy and healthy.

Where are your standards, girl? Don't date people who use drugs, or used to do drugs with their children (!). That is low rent, dysfunctional, horrible stuff.

You get to decide what you will and will not allow in your life. Please don't choose this mess. Get out of there.

Really?

Re-read your post as if someone else is asking for your advice and do what you would advise them to do.

And.... yes, you should leave this shallow and polluted druggie gene pool.  NOW!

smh

I would hate for you to be coming back here in 1/2/5 years time and thinking, "  why the hell didn't I get out then"? So NOW is the time to make that choice. Just think how lucky you are to have that choice.  In a few years you may be so far down the rabbit hole you may never find your way out.  There are four people in this relationship. You your fiance his son and the drugs and by far the strongest member of this family is the drugs. There is no way that given time you will be asked to just have a little try.  You have got to go girl.  Stop looking for reasons to stay with someone who is obviously not the right one for you.
Believe me, if he was, you wouldn't be reading this. You would be watching a box set with a tub of popcorn.

This situation would be a hard pass for me.

Leave them to each other and move on.

Sunshine - I am 22 years a SM of a 51yo SD addicted to booze, drugs, sex... She grew up privileged, has college degree, used to be cute - now she is evil, homeless and dangerous. Love will never be enough to save these folks.  Love yourself and RUN!! Never looking back except to Thank God you didn't stay ONE MORE DAY!!

You're doing well, step by step.  Stay strong,  Sunshine.