I’ve liked this girl for about a year and a half now,side note, she knows I like her, I’ve been her best friend and helped her out of so many bad mental situations. Recently she blocked her ex to try to get over him. And me being dumb decided to ask her after she got over her ex, if she wanted to date, and she said she doesn’t want to move on from someone to someone else. I instantly regretted asking her that but I don’t know what to do. I’m already over bearing to her from what I can tell. I constantly want to text her and I don’t think she feels the same way anymore. I’m losing my best friend and the girl I love because I’m stupid, is there a way I could fix any of this because it doesn’t seem like it. She’s the only one who makes me happy anymore and it hurts seeing our entire friendship start slipping because of me
You’re not stupid. You’re friend needs time to heal. She will decide if she wants to be in a relationship with you. Be patient, my man. Stay strong!
You should just apologise for asking. It may have not been the best thing to say at the time but you did it and you have to own up to it now. Don’t lose sight of your friendship because of what you think might happen. Be there for her still and talk to her about it. If you still want to be with her when she is better then talk to her about that as well. Best of luck
It doesn’t make you stupid, friend. Only human. 
She needs time. And being honest with her just like you’ve been in your message here could help her to understand. Don’t text her constantly even if you really want to. That would be the last thing she’d like and it won’t help any of you. Let her know that you’re here for her but also that you’ll respect her boundaries. Tell her your friendship matters to you. Time helps to heal the wounds.
Hold fast.