I don’t know what you imagine happens when a child turns 18! Do you think that the magic job fairy comes along and offers them a well paid job so that they can go out and rent or buy their own place?
The vast majority of young people in the Uk aged 18, 19 and 20 are living with their families, either full time or part time. If they are away studying at university, that can be 20 weeks a year or less. If they have an apprenticeship, they usually earn a low wage in return for getting training and qualifications. If they are NEET, they are usually sleeping all day , gaming all night , eating all your food and whinging that they don’t have enough money.
So it’s not like they don't live with you anymore, or that you don’t have to financially support them ( unless you are a non resident father of course, then you don’t have to pay a penny ).
And it’s not like you don’t have to parent then anymore, that they no longer need love or attention or guidance . Yes you don’t have to take them to school but you still have to pick them up and run them about ( unless they are rich enough to have a car or lucky enough to live somewhere with good transport ). And they are capable of getting themselves in much bigger messes that they need your help to sort out.
No they don’t have school friends who come over in play dates. They have boyfriends or girlfriends who come on sleepovers and then end up moving in with you. Sometimes with their baby.
I have three teen/ early 20s kids so I know a LOT of young people of that age (probably hundreds ) and not one single one is living on their own and fully independent at 20, let alone 18. Even the ones who have decent jobs at 20 are still living at home “ saving up for a flat “ aka buying a nice car, fancy clothes, a gym membership and going on nice holidays with their GF/ BF.
And apart from all of the above, why on earth are you suggesting that the Op put her own life on hold for FIVE YEARS for a man she has been long distance dating for 8/9 months?? At what point is a woman entitled to put her own needs first ? She doesn’t owe this guy anything except “ thanks it’s been great but it’s no longer working for me, I wish you all the best “.