Is it normal that i like to fuck my elder sister?

I’m 45 and my elder sister is 56 year, she still has an attractive body, her husband died due to medical problem and her children leave abroad due to marriage or work. I use to pass by to help her in case she needs something. One day early she called due to water licking in her bathroom, I want their and worked around 2 hours to fix the problem, I wasn’t expect to spend too much time and have work after that . I asked her if I can take a fast shower to catch my job. I take my cloth take my shower fast and look for soothing to dry myself. I open the cabinet to take a towel where I discover that my sister forgot her vibrator. I look at it and smell it which ma my cock grip. Accidently I turn it on /off, it has a weird engine noise. I run outside the bathroom and pass by my sister room. She was laid on her bed with only a short pink robe where you can see clearly her nipples and huge breast and her long firm legs. I asked her if she has any T-Shirt left from her husband or son since mine became dirty. She want up to give the shirt and I found that she was setting on her panties, which mean that she is not wearing anything..This idea makes me hard more than before. I realize from the color of the panties that it was humid. I couldn’t control my feeling, my dick was getting harder and it was clearly moving the towel to liberate himself my sister look a me, smile and said…what you see in toiled cabinet is normal for a woman leaving alone without her husband. I can understand that woman get horny if they see it but I can understand what make you horny man. I ask the pardon and to reconcile her I tell her that she still have a nice body and lot of man will desire her. Then I took the shirt and left. But since that day I’m still fantasies on my sister and getting masturbate.