I (26F) need advice on how to end a relationship with my boyfriend (28M) of 3 years.

I (26F) have been with my boyfriend (28M) for almost 3 years. We have a great relationship and I love him so much. He loves me too and I know this will devastate him and be really hard on him which is why it’s so hard for me to do. I worry about not being able to find someone else like him. We don’t live together yet but have talked about moving in together and getting engaged later this year.

The reason I need to end things is outside of his control and mine. He has a sibling with autism who will never be independent. His plan is to have her live with him when his parents can no longer take care of her. His parents also don’t have anything saved up for her and she doesn’t get disability or any resources. He plans to financially support her.

I’ve put a lot of thought into this and it’s just too much for me. I love him but I just don’t look forward to the future because of that. We both want kids and I’m also concerned about the increased risk of having an autistic child myself. I know I need to end things because it gives me so much anxiety to think about it but I know this will devastate him. We’ve talked about the situation a couple of times before but I don’t think it’s fair to try and convince him not to be a caretaker to her if that’s what he wants. I feel like this will blindside him and I feel bad.

TLDR: boyfriend and I just aren’t compatible long term but have a good relationship. Looking for advice on how to end things.