Well from a legal point of view, as long as there's no blood between the two of you, then it's fine. Even with a blood connection, in the UK, the law only covers direct relatives such as parents. siblings, grandparents and blood uncles and aunts... by the time you get to cousins that's OK (well from a legal perspective anyway lol).
However, it all depends on how your friends / family may perceive this sort of thing... for instance in many South Asian communities, it's not uncommon at all. But in my family, it wouldn't go down particularly well.