Sorry your feeling so down right now! Please don’t think it’s you as I’ve been on this situation myself before but I’m a girl, so on the receiving end.
I met a guy online around 8 years ago and we spoke for months before meeting. Like you we went on a few dates and then finally tried to have sex but he just couldn’t get an erection at all. Like the girl your talking about, I kinda shrugged it off too and went home that night like nothing happened. I didn’t realise at the time but for him he felt terrible. He took it soo personally and thought I didn’t fancy him and that he had completely ruined everything. For me, I felt insecure too, I thought he couldn’t get an erection because he didn’t like my body, I was thinking all stupid things like ‘am I a catfish?’ ‘Did he just fancy me in pictures’ etc etc. But I couldn’t of been anymore far from the truth. He liked me that much that he had too high expectations that night and wanted to perform amazingly and all of these thoughts for him made him not be able to get an erection. Which is soooo completely normal, most people won’t talk about it but it’s happened to the majority of men I can assure you.
Luckily for me when managed to continue speaking, as weird as it was at first I was a little self conscious so didn’t look too keen I bet and he didn’t want to try to hard in case he pushed me away. We eventually met again and we’ve been together for 8 years. It’s happened a few times in our relationship, mainly at the start and I would get really upset that it was me but it’s just something that happens. I kinda get a feeling she’s not trying as hard now because she may feel the same, like you don’t like her or fancy her or she may have had it happen before and now she’s taking it personal. The fact you said you’ve been on several dates and wanted to meet each others parents before even having sex shows she is into you. That night may have just made her doubt herself more than anything. If you like her, don’t give up on her. She’s clearly not there just for sex or you wouldn’t have waited so long before trying.
She may be playing a little hard to get a the minute to check that you really are into her, us women are weird like that sometimes! Don’t be too keen texting her all the time but make your feelings clear to her and then leave it for a few days, see what she’s says. You can do it! Go for a walk don’t focus all your energy into this because you don’t want to get further down in the dumps, as hard as it is when your in love, just keep going, keep your mind busy and don’t spend too much time overthinking the situation. Try and go back into work and take it day by day. You can do this!