Deadpool
The best advice I would offer you is to obtain US Citizenship. This would give you options if you do decide to return to the UK and things don't work out or you ever want to return to the US. A Greencard is only of value to you if you wish to reside permanently in the US. Much more opinion I could give based on my own experience but firstly, establish a right to return unless you are absolutely certain you won't want to go back.