Beth,
I totally understand how your feeling, I can't stand the pain of never seeing my father again. His passing took over my whole life I can't think of anything else. It's been 4 mts and I cry on and off everyday.. As for feeling guilty your Dad knew how much you Loved him and he needed the mask to breathe otherwise he would have been struggling,and because you love him so much you could not let him suffer.
Trust me I know how you feel!
If you want to PM to talk please do. It's been 4 mts for me and I'm still a mess
Love, Michele