I mean it does depend a bit. And I’ve seen your update that it is your DP who’s won it, now doesn’t want to marry etc
In a lovely relationship, you’d think he’d want to share it.
If you were asking hypothetically as per your OP, I would have said it would depend if it was the person with the financial power generally in the relationship who won it (ie that person should definitely be sharing it). If one of you had stepped back a bit from work to care for children etc and that had impacted finances, that would be a factor - so if the person still able to work full throttle won it it’s fully joint, if a SAHM or part time worker won it, I’d say they had good cause to see at least some of it as just theirs.
If someone who needed to flee DV won jt, or who was being financially abused, then definitely all theirs!
I would hope in any loving relationship the person winning would to share at least most of the money with their partner, at least in terms of buying something joint with it (whether something for the house, a holiday etc) or investing in joint savings/ paying off a mortgage, if not literally splitting the money/ putting all in joint funds.
I wouldn’t expect a working husband who has two children with their fiancée to say “no this is all going on a jolly for me with the boys/ a bit of new kit for my personal hobby” or similar.