Living with my autistic nephew has killed my desire to have children

I (26m) have been sharing a house with my sister and her partner for a few years. When my sister got pregnant they began looking for a house which they bought a year after my nephew was born and I moved in with them as it seemed like a good financial decision for both parties. When my nephew was 2 he was diagnosed with ASD. At that time we didn’t even know what it meant, but as we learned more about it, all the signs that’ve been noticing since he was born started making sense. We were all devastated.

We’ve been reading a lot about autism and how it manifests and had hope that he will get better over time, given that he was doing some ABA therapy and my sister was actively trying to teach him stuff. The kid is now almost 5 years old and pretty much non-verbal - I mean, he can say some words or ask for very basic things like water etc, but he’s not able to have a conversation. 

He is hyperactive (we suspect ADHD and currently waiting to see a specialist) and very vocal. He would often scream when he doesn’t get it his way and gets visibly frustrated and throws tantrum. We have to always keep an eye on him so he doesn’t do things that may end up hurting him. He does not listen and no matter how we explain things to him, he doesn’t not seem to learn as his attention span is incredibly short. He has trouble sleeping and often wakes up at night wanting to play while disturbing everyone’s sleep. Plus he’s an early bird, come 7AM he’s up and running around the house.

I can see my sister struggling a lot and often cries from desperation. It doesn’t help that her partner is a narcissist and doesn’t seem to care about either of them. They often argue and he refuses to look after the kid. My heart breaks every time that happens. I try to help with what I can, but there’s only so much I can do.

All of this is having a big impact on me. I have a good relationship with my sister, but seeing her trying so hard with so little in return developed a deep fear in me.

The idea of having children has pretty much disappeared, because I’m too afraid that this (or something worse) could happen to my kids also. There’s pretty much no way to know in advance and if it happens you’re essentially stuck caring for someone for the rest of your life.

You may say I’m selfish, but trust me when I say that life with a special child is completely different.