because they think we dishonour our culture
In 'your' culture your sexuality and your life are the property of your male relatives who can trade it or sell it (or dispose of it) as they see fit. "Honour" is a mighty fancy word used to cover a very ugly reality. Don't kid yourself.
You might want to dump Pakistani culture and embrace British/Western culture where you have to make your own important life decisions instead of being used as a commodity for the prestige of male relatives. If they won't accept your Polish boyfriend it's because they've never accepted you. Again, face the facts. I might sound harsh but sometimes that's what's called for.
If this Polish man means something to you, you need to be able disappear and say goodbye to your culture forever. You might think your family isn't capable of violence against you but there are lots of dead Asian girls in the UK that thought the same thing.