If I said to you, stay away from him... Would you be willing to do it?
Or, how bout... Just be friendly with him but neither encourage nor discourage?
Personally, I'd suggest ending the association until he's capable of getting his visa here (uk) cos then you can meet on an equal footing and it saves you being drawn deeper in.
Getting the relevant permits is his responsibility, not yours. Coming on hols here and having somewhere to stay is also his responsibility, not yours (I mentioned this part in case you were thinking of accommodating)
Not to be harsh but based on the fact you're calling him your bf... No matter how well you think you know him, reality is, you don't. He could be legit and if he is, then the onus is firmly on his shoulders to do the necessary.
Just bear in mind your personal and emotional safety. Bear in mind you only have his word on stuff. Exercise caution.
Whilst true that if someone wants to make a fool of us, they will... being careful can sometimes make the difference between getting hurt n disillusioned and, not.