Spook, it's such a relief to have news from you, several of us have been quite worried. You sound as if you are beginning to move on and planning to move away is an enormous step in your emotional journey as well as the distance in miles. It sounds as if Ibiza is a place where you can heal and be happy, and it sounds just wonderful for your sons too.
Can you make sure that the house becomes your house, so that h cannot just bowl up there anytime he likes and upset your calm. He ought to stay elsewhere when he comes to visit. I'm so glad your MIL is beginning to see how badly you've suffered. Perhaps to begin with she assumed her son would come back to you with his tail between his legs.
The time between now and September is an ideal period for double checking your thoughts to ensure this is really what you want, as well as time to make proper preparations. It will give your h time to take on board the reality of what is happening too.
Please carry on posting, you have been missed for the last three weeks. Besides which, how am I going to come to Ibiza and visit if you don't let me know where you are?