Living alone after marriage feels worse than living alone before it

I lived alone in Delhi for six years before the wedding and I was fine. I had a routine, friends, a gym, and I liked my own company. Now the flat has her things in it and she is not here. Her mug, her side of the cupboard, the plants she asked me to water. I water them and feel absurd. Weekends are the worst. Our friends are couples and inviting myself as a half is strange. I am not depressed, I function, I work. I just feel a low-grade loneliness that I did not have before I was married, which makes no sense to me. Does anyone else recognise this?