If he’s reliant on it, then that’s classed as an addiction.
Has he expressed any remorse, responsibility, desire to get help/stop?
The first thing to accept is that you have no control over this situation. You cannot get him to stop no matter what you say/do or how you react. It needs to come from him, and with addicts it usually comes from a “rock bottom” place.
What you can do is work out where your boundaries are. You can leave, it’s not up to him if you can or cannot go back to the UK, that’s your choice. Or you can stay and try and support him, but consider my points above and understand that it’s going to be hard. You will need to educate yourself, you will need support and therapy to help you, you will want to cry and scream and have to find strength you didn’t know you had. Ultimately, this will drain you, can you support him and be the best mum you can to your child, and shield your child? If not, then your child will suffer. And that means you NEED to leave as your most important job as a mum is to protect your child (yes, even from their father).
Have a look at this, it might help. SMART recovery have some zoom sessions for family and friends of addicts too.
https://www.ukat.co.uk/help-guides/dealing-with-addiction-denial/
But please, whatever you do, please protect your little one as a priority. The trauma that can be passed on to them is huge, and trust me when I say it WILL have an effect and you WILL be having to deal with that trauma and the resulting mental health struggles they’ll have when they get older.