What on earth is wrong with me (M19)?

So yesterday my gf (F19) wasn’t really replying as often as usual. So I’m like right, that’s grand, she’s just busy. But at the same time every time I messaged her, she wasn’t that talkative in her replies so I’m like right she must be really busy today and doesn’t have much time to talk.

All day though in the back of my mind all I can think is there must be something wrong. I shake off the thought because I keep telling myself to trust her and if there’s something wrong she’d tell me herself. This worked until around 9pm last night when I asked if everything was okay and she skipped the question completely which concerned me. Then she was like “we can FaceTime if you want”. So I find this a bit odd just the way she phrased it but I move past it and I’m like yeah I’ll ring you now.

Then she goes “wait don’t call yet, there’s murder downstairs” so I tell her that’s grand and just to let me know when is a good time. So a bit later she rings and she seems perfectly fine, in a great mood, laughing, cracking jokes, asking questions, but I’m like shivering and kinda feel like there’s a massive lump in my throat. So I muscle through that but, we FaceTimed so late at night and well in my house everyone can hear everything from every room no matter what so I couldn’t match her energy or volume in the call since she doesn’t have to worry about making too much noise or anything.

So by the end of the call I just feel a lot of dread and guilt and I can’t really pinpoint why, but I stayed with her on the call until about 2am when she said she was going to sleep and told me to go asleep soon. I don’t know why but I nearly started crying right as the call finished. It felt like I’d never see her again which is ridiculous but that’s what it felt like.

I don’t know what the hell is going on with me, why can’t I just have a normal day and a normal call why do I have to be like this?

It might be worth mentioning that we’re long distance atm due to Covid, usually we’d be able to see each other every weekend but that’s not possible.

TL:DR I feel really ashamed and upset over something but I can’t tell exactly what it is.

EDIT: Thank you everyone that’s given advice and helped me out, it really means a lot! :)

EDIT 2: I’m seeing a bit of confusion in the comments about the “theres murder downstairs” part, where I’m from that’s just an expression to say there’s trouble like people are arguing