The thing with a lot of these suggestions are that OP is doing all the legwork. Why on earth should she be doing all the investigating into his housing options, given the reason he for asking him to leave is his lying, utter lack of respect for OP and his family and home and poor attitude? How does sorting it all out and paying for it all teach him anything?
He is an adult now- he can vote, get married, join the armed forces... and be tried for breaking the law as an adult. He is a young adult, but an adult nontheless. This attitude is exactly why we have so many young adults utterly unprepared for adult life. Actions have consequences. Shielding young adults from them does them no favours in the longer run.
I think there are too many posters on here who are suggesting quite an infantilising approach. OP is to find out if he is eligible for supported living/a council house/ find a flat for him and pay for the deposit, plus possibly his rent for 6 months... do we think that he’ll start paying the rent after 6 months? Do we think he will look after the flat any better than his current room? I doubt it- not his deposit to lose, not his credit rating being messed up if op agrees to act as a guarantor. And as OP has sourced and paid for the flat, why would he not assume that OP would do it again? Or allow him to move back in, as she feels guilty re being responsible for him ending up homeless (though actually, if he did then it is almost all his own fault). She’s already shown him that she’ll cushion him almost completely from any consequences, what would be different the next time?
OP, you’ve tried discussions and he doesn’t keep to his agreements. No more being nice or negotiating. The rules are along the lines of:
1)he either gets a job or goes into education. He has to prove that he is properly and actively job hunting (not you finding the vacancies and nagging him to apply). He needs to sign-on in the meantime;
2)whether working or on benefits, he contributes a proportion of his income towards his board and lodgings;
3)he will keep his room clean and reasonably tidy;
4)he will do his share of the housework- to an acceptable standard- and do his own laundry etc;
5)he will be respectful of you and all family members- no shouting/aggression etc. He will return home at a reasonable time due to his younger siblings. If he is late, he will be quiet and considerate of those who trying to sleep;
6)he is not to eat family meals etc- he can eat with the family, but he cannot empty the fridge at lunchtime leaving nothing for anyone else. It’s not fair.
7)Any further stealing will be reported to the police- and mean it.
He agrees to these or he moves out within x time (1 month or 6 weeks or something). If he agrees but doesn’t abide by the rules then he gets x weeks notice to leave. Where he goes will be up to him to sort out. BUT you have to be able to mean it. If you don’t, there’s no point threatening something you just will not be able carry through.
If you pussyfoot around him, ask him to leave but sort it all out for him, do all the legwork and pay for it all- do you think it will change his attitude? I think the attitude will remain l, just in a different location (which you are finding).
I speak from some experience.My brother was awful, lying/ drinking/ drugs/ aggression/ stealing. We had same upbringing- only “trauma” was my dad’s serious illness, but nothing terrible and we had a good childhood, on the whole. He likes to be “the big I am”, fell in with the wrong crowd. I really do think most of it is personality, tbh. Nothing worked-they tried counselling, they paid for family therapy, negotiations/rules etc. My brother would it’s lip service to the rules or any agreements made. He made life very hard for us all. My mum acknowledges that by not addressing things effectively sooner (due to fear that he would end up on the streets/in jail etc) they made things very tough for me (and themselves) and did not help my brother turn his life around.
He stole from my grandmother- valuables which amounted to a sizeable sum- she gave him an ultimatum he knew she meant- he had to come up with a plan within the month to show her what he was going to do to sort himself out- he had to get a job (or at least show he was looking and doing so seriously) or enter education. Failure to do so would result in her reporting him to the police which, given the sums involved, would probably lead to a fairly serious charge. This seemed to give my parents the impetus to back up this ultimatum. He joined the army as a result- it did make some changes for the better. Unfortunately, it didn’t go so well after he left, but that’s another issue.
My point being that if you negotiate/gave a chat etc, without any real intent, he will know and carry on in whatever way suits him. And why shouldn’t he? You facilitate his behaviour.