I feel like I missed my only good chance at a nice relationship because of low self-regard

Two and a half years ago when I started university I really wasn't in a good mental place because I've been struggling with it for years now. At that time there was a girl in my class that I did find attractive from the start. Then it turned out she was a good friend of one of my good friends so we 3 occasionally talked together (it was very rarely). The more I got to know her the more I liked her but my mindset just sucked. I thought I wasn't good enough or worthy of even trying. One time she needed some help so she messaged me and then thanked me really hard for helping and then did that again after class. After that I think she started constantly glancing in my direction and that continued for a while. One day out of nowhere after a lecture after we haven't talked in a while she asked me what my cats name was. I simply answered with the name then she said that she asked because she thought my cat was cute and I just responded with "Ah okay!". This moment has been constantly playing in my head every once in a while just like right now. I can also somehow "relive" moments in my head: from what I saw, what I was thinking, sometimes emotions,... and that just eats away at me so many times (but sometimes it can be nice with good memories). A bit after that we had around a week off and one of my friends started messaging her (the first couple messages were when he was extremely drunk). A day after she ended the conversation with "You seem like a nice guy but I don't want to meet anyone new right now". The friend obviously showed me that screenshot and I gave up. I was dead certain I was just making stuff up. Shortly after that I also learned my father got cancer and that I have a basically guaranteed chance of getting it as well a bit later in life (it's been passed down for many generations already and I've inherited a lot of my father's health problems that have shown already)... which meant I basically already finished half my life before the possibility of it ending badly. That absolutely mentally destroyed me. Whatever few good things I felt about myself were completely gone. I felt like my life was just worth nothing. After that I just completely stopped talking to her even avoiding her. A year after even tho I think I still could have fixed it I thought that it was too late and I already fucked up too badly. Around a month ago I overheard that she didn't have a boyfriend back then but does now and honestly hearing that made me feel better. She is happy now with someone and it feels like some weight has been lifted off me.

So why do I think this was my only shot? Because I think she liked who I was instead of just my appearance. And to this day all I've heard is that my face looks like shit by everyone in my life. And of course appearance is the only thing that matters from the start.

I was over all of this not long ago but I've been having a hard time again and I'm really trying to make myself believe that I am worth something... that I can be happy with who I am... but that time always plays in my head and tells me how much I fucked up.

I am just writing this post to get all this out of me since I have no one I can talk to about how I feel without having to worry about them changing how they act when around me and I'm too afraid of therapy.

I will probably post more things on this subreddit for the same reason... just to get it out there and to try to put more things behind me... to get it off my chest.