I think you did the right thing. He is not a child anymore. He's a man. You don't need a man living in your house, especially if he is doing illegal acts.

Personally, I would never allow him to move back in. Again, he's a man. Let him get a job and roommates if need be and make it on his own like most of us had to.

I agree, you did the right thing. I know it might be hard on the 10 year old however it is better that he does not learn and think this kind of behaviour should be tolerated. Counselling would be good for the family however not with the planned outcome of this young adult moving back into your home, but with making the relationships work because your girlfriend will always want him to be part of her life. I can't believe that you put up with it for so long, especially the gross factor of him collecting urine in bottles under his bed (yuck).

I have a sense that you feel like you are being used as a meal ticket by your GF and not a true partner. You sound resentful and said she cannot afford to live anywhere else, do you want her as GF and living with you? Do you feel that she staying just because she can't afford to go anywhere else?.
If you want the relationship to work and you want her as a partner in life couples counselling. If that is not the case I would cut ties before it even gets worse.

Congrats on doing the right thing!!!

I'm going to respectfully disagree with the other posters. Let me explain. You are not the biological parent and the discipline etc should come from the mother. If you have a line in the sand and your GF will not stand with you and enforce that line on principle, then you are barking up the wrong tree. Your very first mistake in this situation was believing that you could "influence their lives" and be a good role model without being the biological parent. That rarely works with older children such as the 18yo. The kid will absolutely never respect you if the mother is not the one laying down the law. If he feels that these are your rules and not hers, you will not get any respect and only resentment and grief. That's a fact. I believe you should decide now if this relationship is really worth it, because she is the bio parent and should be the one handing out consequences etc and you act as support. But, she seems to be unwilling to enforce anything so it pits you against everyone in the house, your GF included. I have never found it to work the other way around as you are describing. If this mother is passing off parental decisions and discipline to you, you are screwed. My advice is go to counseling with her because what you describe as the law of the land should be enforced by her not you. You should be backup for her not the reverse. I do believe if she does favor the older son, you are setting yourself up to be the "bad guy" and your relationship will gradually disintegrate.

No, you were not wrong to boot his useless POS ass out of your home, family, and life. Now that he is gone, he needs to stay gone IMHO.

This POS man child needed a true man of character to set the example for him and to hold him accountable for his behaviors. You did that, you stepped up, he didn't, cut your losses and keep him far, far, far gone from your daily life, your home, your relationship, and the family that you, SO, and YSS-10 are making. You may have time to salvage the YSS-10 and if this lady is THE one then good luck.

This is of course contingent on your SO stepping up and being your equity life partner and acting as your partner in keeping her foot and yours up her eldest kid's useless ass and raising the younger one with rules, discipline, and consequences if he violates the rules.

I became Dad to my SS-22 when his mom and I started dating when SS was 15mos old and married the week before he turned 2yo. We worked as a team to get him out of HS on time and when he refused to go to college (on our dime) or get a job we turned him into our beck and call boy/chore bitch and worked his ass off until he enlisted in the USAF and reported for BMT. My wife and I had out collective feet up his ass but if she had balked I would have put both of my feet up his ass and dropped him off at induction. My example of a man of character and integrity and the effective example of the life partnership his mom and I share countered the toxic bullshit of the shallow and polluted end of his gene pool and made the Sperm Clan nothing more than an effective example of what not do in life. The Skid is doing incredibly well in his USAF career, is progressing on his BSCS, and is trying to influence his three younger also out of wedlock Sperm Idiot spawned half sibs to be more than their Sperm Idiot will ever be.

Taking this POS druggie idiot back into your home and life would do him no favors and if anything you need to call the police and let them take over keeping the big foot of the law up his useless ass for his drug use and interfacing with scum dealers. JHC, the idiot hat bottles of piss under his bed for God's sake . Keep him the hell gone. Way gone, for ever. PERIOD!!!

Stick to your guns.

IMHO of course.

Good luck.

This statement is the root of your problems,

"I had them move in with me in hopes I can be an influence on their lives but was too late to SAVE the then 15 year old"

You moved a broken family into your home to be their knight in shining armor and "save" them. People can only be rescued and accept help if they want it. The now 18 yr old obviously never wanted your help or saving and probably resented it.

He's out and needs to stay out. You did the right thing, continue to do the right thing by encouraging him in the adult world. You do not need to get counseling with the 18yr old, he needs to "man-up" and live his own life. You and gf could use some counseling though.

"Is this worth fixing?"

I'm not sure what you're referring to. The broken family, the relationship with the 18 yr old, moving him back in? I think you really need to ask yourself if you really love your girlfriend and want to continue building a life with her or is this family just another project for you to "fix?"