why is it so hard to fall in love with someone else after getting heartbroken

For some context, I used to like this girl who is also my best friend for 5 years, and then out of nowhere, she just sent me a message and started confessing her feelings to me, feeling happy and fulfilled, I confessed my feelings to her too, then she started to proceed talking about how she likes this other friend of ours way more then me and asked if she should confess to her , and then, me being a straight up DUMBASS said yes because I didn't want to see her sad yk, our friend accepted her confession, and I was left there heartbroken while she said it wasn't anything personal.

P.S: I've known her practically my entire life and I've always been by her side comforting her whenever she sad and etc (guess what she never did that for me), but it's not because of that, ITS BECAUSE OUR FRIEND IS HER VIRTUAL FRIEND WHO SHE MET ON FUCKING TIKTOK 6 MONTHS AGO (at the time she had only know them for 3 months) 

Im already over it, I just wanted to rant abt it and hear someone else's opnion