Waalykum salam sister
Thank you for your question
It is indeed difficult to tackle such sensitive issues especially when the opposite person is not ready to discuss it.
For your situation I would suggest
1- Speak about some other cases and issues and how people’s lives fall apart because either partner was cheating on the other. This will certainly ring some bells and he will be able to relate and InshaAllah bring some changes!?
2- Keep him busy. Life as husband wife is to enjoy. Make sure your daily life is jam packed with exciting things where he finds lesser time to sit behind the screen. Also, loving him and giving extra attention might result into you some extra value for your relation together
3- Make a lot of dua for yourselves. Set aside charity, and make sure you spend plentiful time speaking to Allah and pour out your heart. That way you will feel better and InshaAllah Allah will help him understand better
4- If things don’t work- God Forbid- try speak to some who he listens and let him help further. Your local Aalim can help InshaAllah