[TW] Need Advice

TRIGGER WARNING: Death, Cancer, Medical Problems (mostly epilepsy)

My gf means everything to me. Honestly, she means more to me than that. So it hurts even more when I have these nightmares about her dying and my life after that.

My gf suffers from a few medical and mental problems, with the biggest being epilepsy. She's had seizures that had been so bad I wasn't even sure if she would be okay. She had gotten a service dog a few months ago that helps detect her seizures and he's definitely helped more than I honestly thought he would.

My nightmares, however, never make epilepsy the cause. It's almost always cancer.

To sum up exactly why cancer is the usual cause: Last year, my gf's younger sister had a cancerous brain tumor and she died only a couple of weeks of her diagnosis. My gf and her family were torn and it was really hard to watch them go through it.

I can't help but become worried whenever my gf feels bad because my mind can't help but jump to the conclusion that she will suffer the same fate her sister did and I'll have to raise our kids alone.

What makes matters worse (in this particular situation) is that I'm currently pregnant with twins. And this is my first pregnancy that I had as much control as an average pregnancy allows. My gf and I are so excited to have twins but the fact that I could lose her at any moment and have to raise four little kids on my own is terrifying. I don't think I could do it.

I know things can happen and I should prepare for the worst, especially since she has epilepsy, but I don't want to live in constant fear that I'll lose her. How do I stop having these nightmares?