Wa alaykum salaam
Thank you for your question. You don’t have an Islamic right to make your husband stay. But having said this a number of things are important to consider in the situation you have outlined. It seems that your husband is in the middle of more than one responsibility and it is key that you have a good understanding of the pressures he is under. Conversely, it is also important that you communicate the pressures you are under, but not in a conflicting way or as an outburst. Maybe agree to see how the first stages of the separation go without making a firm plan for the 2-3 years. If you can speak with his parents as well, as a family and cone to a decision, then that is even better. Many times parents can be more understanding than we realise, especially when it is their granddaughter’s wellbeing. A family has to make sacrifices for each other and in difficulties they have to be strong for each other too.
May you always be successful and may the treatment go as planned.