Caregiving is in the same category as marriage and parenting.  It's likely one of the most difficult undertakings you will encounter.  There may be many days when it is hard.  Acknowledge the difficulty but don't wallow in it.   No, you are not being selfish when you complain, you are being human.  Do not complain to the care recipient.  Seek out help, find a caregiver coach and get help with your caregiving responsibilities.  Energy flows where the attention goes.  Savor the moments that are sweet and wallow in that.