Among the many things I've done to try and copy what is normal and fit in, finding a romantic partner and dating has been one of them. I've had positive experiences like finding an incredibly caring and thoughtful boyfriend who loved and wanted to marry me, and very negative experiences like being abused (both different people). Positive or negative, all of my attempts at romantic relationships have ended due to me breaking it off because I reach a breaking point where I can't cope with how frustrated it is making me to deal with it.
I think I just hate everything about it. I hate the attention they give me, I hate that they always want me to pay attention to them back, I feel uncomfortable with affection and I hate being physically touched, I hate the sensations of kissing and things like that, I hate having to sacrifice my personal time for somebody else, I hate spending more than an absolute maximum of 10 hours around one person. It just drives me crazy, it makes me want to tear off my own skin and scream.
Understanding these things about myself has been part of understanding my own needs, and that I do NOT have these particular needs. Even a partner who gave me lots of space would be too much, I'm happy with just a pool of low maintenance friends who respect my boundaries.
As an adult, it's hard because the world is structured around married couples and families but it is not impossible and there are many people out there who live happy and fulfilled lives by choosing to be alone.
On an end note, I want to clarify that I know my experience is not universal to all autistic people. I see autistic people on here who like to have their partners to support them, who are happily married and I'm glad for them. It's just not for me and I'm sharing my experience because maybe it can help somebody to feel less alone.