Even in Denmark the AVERAGE age to leave home is 21 and as an average that means some younger - and some older!
Saying what his income is doesn't mean we know if he could afford to live away from parents, my understanding is the cost of living in Denmark isn't exactly cheap, plus you're giving us amounts in euros when the currency is Krone and frankly I'm not faffing about converting across 3 currencies to try and understand the cost of living for young adults there! (If there's any other Danish resident mners can help I'd be interested though).
Plus you moving out at 20 unless it was on your 20th birthday meant YOU were living at home at 20 too - so just 10 years ago and makes you no different!
I agreed in my first post it should have been discussed with you, but it's really not unusual in Europe to stay living with parents until in full time, fully paid employment. You knew this, but ASSUMED it would be left to the guys mother to cover this issue.
"He has lived together with his son for the past 18 years. It was not new to this thing." Even more reason why this is not a huge leap for your partner.
As an aside...to be honest it sounds like you've both rather rushed into things if it's only 2-3 years since he split from their mother!
Am I right in thinking you only lived together around 6 months before you bought?! Why?! That's crazy! That's nowhere near long enough for "best behaviour" (by both of you) to wear off and to rub each other's corners off. The saying you never really know someone until you live with them is so true and I would say you need to live with someone AT LEAST a year before you can know if your compatible doing so - again what the hell was the rush?!
You've actually misrepresented the situation when you've made comments about stepson "always living with mum" at the point you came on the scene things were still in a state of flux, regardless what your partner said any sensible person would have assessed that much.
"You can’t force someone to accept your family in your house just like that" you're COMPLETELY missing the point! As far as your partner is concerned (and I'd be the same) both you AND his son are his IMMEDIATE family! You seem to not get this at all! You're acting as if once his CHILD hits 18 he should no longer be welcome in HIS parents home - regardless of that parents sex!
Several pps have said - your kids are your kids ALWAYS that doesn't cease when they hit ANY arbitrary age. My brother and sister have both bounced back to living with my parents - including with their own children - when they've been having a rough time or there's been hitches with house moves etc. With my sister I don't always agree with it as she does take the piss and is constantly needing bailed out, but I can see it from my parents perspective too of that's still their child and if they're able to help they will. Bro's only done it twice, once when he first became a Lp and he was adjusting (he was already separated from child's mother when she died in a car wreck) and also supporting a bereaved child. Then again when there was a hitch when he was buying his house. I
"You've been had. You are the new skivvy with a younger body and no children if your own to distract you from tending to his needs." This too is entirely possible! But then all the more reason NOT to buy a house so quickly with someone you barely know!