I'm struggling so this post will be a bit of a whine

I am posting because I know some of you will understand and I don't feel I can talk about this with friends & family. And maybe some of you can give me a push to change my attitude.
DH and his ex (UBPD) have joint guardianship of SS18, who has development delays. He is living 50/50 between parents. A few days ago, DH's ex sent an email saying she and her BF are going to Europe in June so we need to take SS18 an extra week. As usual she didn't ask DH, she just sent and FYI. DH usually agrees to any additional time with SS18. We never ask his ex to take SS18 on DH's scheduled time.
The problem is that I'm having major surgery in June. I'm nervous about the surgery because there's a good chance the recovery will be slow and difficult. I have been told it will take me several months to get back on track. I would love to have time to recuperate in peace and quiet. If SS18 is at our house for most of June, this will be difficult.
I love SS18 and he has many wonderful qualities. He is also highly anxious and his delays mean he acts more like a 12/13 year old. This past year, he has taken to eavesdropping on conversations (sometimes immediately calling his mom to report what he hears) and to lying. He uses all the money he makes from work to buy junk food and coffee -- both of which cause him to get wound up, resulting in him bouncing around the house, yelling, being silly and then when the sugar and caffeine wear off, he crashes and is grumpy and tired. These emotions come through in lots of noise and conflict in our home. He also craves attention and
[url=https://bpdfamily.com/content/communication-skills-validation]validation[/b][/url], so often follows me around the house, talking outside the room I'm in if the door is closed. If he can't see me, he will ask DH "where is NorthernGirl, what is she doing, is she mad at me?" DH says that comes from his mom spending hours in the bedroom when she is depressed.
When DH told me about the email from his ex, I asked him what he was going to say. I let him know that I would prefer not to have SS18 around for most of the month after my surgery. His reply was "I hate being in the middle." He said if he said no, then his ex would have to send SS18 500 miles away to her parents as she has no other back-up. SS18 would miss school and be bored (his grandparents do very little and have no expectation for him to do anything.) So DH sent his ex an email saying we would take him the extra time.
I am very sad. I feel as though DH made the decision best for SS18 and best for his ex. I know I could have made a bigger deal of this and told him that SS18 couldn't stay an extra week. But I didn't because I know DH wouldn't have understood. So now I have to live with the fact I didn't push him to say no. I will probably head to our little cabin by myself once I am able to travel after the surgery. DH says "don't worry I will make sure SS18 is quiet and helpful." I don't believe it, mostly because DH struggles to apply any consequences with SS18 and DH lets guilt guide his decisions when it comes to his boys.
As I'm writing this whine, I realize I need to look at more positives. Maybe SS18 will do better than I'm giving him credit for. With his mom out of the country, he won't be inclined to eavesdrop to report to her, and he will have less reason to lie (he is often lying to cover up for her.) And maybe when DH understands how serious the surgery is (I think he believes it will just slow me down for a few days), he will make sure that SS18 lets me recuperate in peace. Fingers crossed.