A Parenting question...............I think?

So here is the question. When do you cut the cord?  Not the cord between Robbie and I- seriously- it may never happen. The cord between siblings. The bond between Robbie and Lexi is................. amazing. As I attempt to write this post Robbie has come down from watching a movie with Lexi. He is reciting some movie line I do not recognize. She comes down and ushers him back up to get to sleep- asking - Lexi's room or Robbie's room , because she knows he will not fall asleep by himself and I have asked for 10 minutes to write.   It is a beautiful relationship- that of siblings.   Love you Suzie Q and Dummy Piggy Robbie- private joke- only my siblings will fully understand. And yes my brother, husband and son are all named Rob.
Robbie has made so much progress regarding speech and communication. Our biggest challenge has been socialization- friendship. He seems ready and interested -sometimes- when it is on his terms. If you want to do what he is doing- or play along side him- he is game- otherwise- ............not so much. We attempted a play date with a friend of mine, who has a special needs child, and lives in the community. My hope was/is that Robbie will make a friend locally. Someone he is happy to see at community events. Maybe someone he wants to build Legos with. To be fair, it was the first time in a long while the kids had been around each other. However,  Robbie had been prepped. I had shown him this boys picture and we had talked about the up coming play date. His ABA therapist had also mentioned the upcoming event.  Robbie is a creature of habit- as many of us are. The change was too much. Having someone else in his space, with his things, making demands of him was too much.  Honestly, it made me sad. My hopes were high that finding a friend would work out.  I was also a little embarrassed by his behavior. Something I haven't felt in a long time- even when he was spinning in circles, barefoot, digging his feet in the dirt in the softball field, while I was attempting to watch Lexi's soccer game on the field close by. Those events don't phase me. They are part of Robbie. We refer to it as "getting the stimmy out".  The bad behavior with this little boy at our house stuck with me. I know myself and try to give these situations a bit of time before I write about them. The problem in this case is mine. Robbie didn't want to make a new friend that day. No excuses. He simply wasn't interested. I am the one who was sad that it did not go as planned.  He is happy- I think. He has his family.  A brother, sister, mom, dad, and dog. He has school- where the routine is familiar and there are familiar faces. He has had the same teacher for 3 years and the same classmates for 4+.
I look back on my life and think- do I still value the friendships I made at 8 years old? Do I even remember them? A handful. A select few I cherish. I met my best friend at 15.  Many of my closest relationships were made in college. So - is it that important to push friendship at 8, especially for a special needs child. And when do I let Lexi fly on her own? She has made some friendships. She is 6. One of the nicest parts of her friends is, they are kind to Robbie. Are they are too young to realize he is different or is he just " Lexi's brother.?" I think, he is just her brother.
This weekend I am torn. Robbie's school has a book fair/ dance/ pumpkin decorating party which I was thinking about bringing him to. 2 out of his 5 classmates will be there. They had gone last year and both loved it. Lexi has been invited to a birthday party by our new neighbors at Pump it Up.  Pump it Up is Robbie's favorite place. Robbie was also invited- as a tag along. Do I take him him to a place he loves, with his sister- who is his favorite person- or do I take him to his school for an event he may love equally- or hate. Who will be crushed more if he doesn't enjoy the "socially appropriate " event- me or him?  What will make happier?  I think I may have answered my own question.........................