I'm guessing this discussion has gone through every permutation at this point ?
I would imagine that this young man would like a 'proper' relationship with someone at some point - he comes from a culture where marriage and children are not just highly valued but it would be considered abnormal to not find a wife and procreate.
Obviously times change and people buck their cultural / religious heritage but generally speaking why wouldn't he want love and a wife and raise kids of his own who all live together?
OP is older, has had her children who are now young adults, really likes the man but would like a more casual LDR it seems (sorry if I'm getting it wrong) and certainly doesn't want to risk marriage and possible exploitation for a UK residency visa / passport (being one of the added attractions or interests for any Moroccan man, as at the very least it widens his horizons, this is undeniable).
I would predict that what both people want in the long term is different and therefore that this is what would cause issues and possible ill will. Plus there's the age gap which isn't a terrible thing but could cause issues, there's the cultural / religious differences that could cause issues, there's the kids not being so keen, and there's the geographic LDR situation which also could cause issues.
That's a lot of setbacks. Setbacks that many many people overcome but many others don't.
I would predict if this relationship continues that one of two things would happen - either it will naturally develop into conflicts of interest and ill will and then fizzle out -or- OP will relent and decide to marry him or move over to Morocco herself. If that happens, it will be besieged with difficulties as neither option (him coming here, her going there) is particularly easy.
Zero judgement or prejudice from me, I'm just looking at it in terms of how situations unfold usually. I hate to say it to the OP but looking at it in terms of stone cold reality, it's probably not going anywhere. Maybe just have a bit of fun whilst there's the sexual attraction chemistry thing and expect it to fade out?
Also, check in with your conscience and him that you're not 'using him' because if he has unspoken expectations, then it could be a little bit cruel to kind of know that and disregard them. The man has feelings, hopes, and dreams.
Also check in with yourself, how you would feel if this was a British man saying these things and wanting to go to Morocco for a booty call with a girl he enjoys but isn't going to help her come to the UK or take it any further? It wouldn't look pretty would it?