How do you stay just friends?

I know that what I'm about to say might be just something that's wrong with me, and I understand that, but here goes.

Back at the end of April, I had my first breakup, she broke it off cause I was being stupid (I'm sure if someone wants to know the story, I have it somewhere in my profile) and I went from blaming myself, to being angry, to numb, to now that she talked to me again a few weeks ago, i feel guilty and just generally, I despise myself (but that's a separate issue and I'm trying to get depression medication) She said she wanted to be friends again cause I'm a "really fun person to hang out with" and for a second I was happy.

Fast forward to a week ago while working with her brother while helping a family friend, he invited me over to their place to swim and I accepted, she wasn't there but I was good friends with her family and I wanted to rekindle that, except the whole time I felt guilty and had panic attacks, but I tried my best to hang out.

Yesterday, at our martial arts class, which is where we see each other each week, I asked if she wanted to hang out, she accepted, but also said that there wasn't a chance at romance. I wasn't trying to consider that again right now, and just wanted to be friends again for the moment, but it's been bothering me.

How can I promise myself that I won't feel pain each time we hang out, that I won't try and be more and end up pushing her away again. How do I keep sane when I know I'm going to be an idiot and try to be close to her again, while also knowing I won't get that.

Maybe it's the depression, I can't really decide on what I want, I don't know where to go.