Hey, it's okay. You were vulnerable with him. I believe that people appreciate that far more than they appreciate a bullshit positive perspective. Are you a terrible person for having your own intense emotions around suicide? Of course not. Your feelings are absolutely valid.
That being said, perhaps talking to him about your own suicidal feelings could have waited momentarily, and responding with more of an understanding of his perspective would have been helpful. I know when I open up to people about my suicidal thoughts, I am not looking to be deterred, I am looking to be heard. Seems like you did offer that up to your brother. However, for all that everyone here absolutely hates anything pro-life, I do believe the goal of your support and unconditional understanding should be to help him out of this rut. I think us pro-choice people, as a collective whole, are far too quick to give up. Of course there are instances where CTB may be the only foreseeable route to take, but for your brother's sake, really exhaust your options before you encourage something like that. As of now it seems you are just relating, which I believe is more helpful than some fake positive sentiment.