My mother's remarriage: My mother married my best friend

My mother went out with a strange excitement and was somehow heartwarming. I was thinking that I would be able to continue to be next to me and see my mother's melting sweet smile forever... One day, my mother suddenly confessed, "I'm married." What's more, his partner is his best friend Tatsuya. It was shocking, but when I saw the two of them smiling happily, I couldn't say anything... I see, my mother has become Tatsuya's wife...