I joined a Saturday running group for time alone, and my girlfriend signed up the next week

Three months ago, I joined a Saturday morning running group. I am not fast, and the group is not particularly serious. We meet at a park, run a few miles and drink coffee from paper cups afterward.

I loved it almost immediately.

Part of the appeal was that nobody there knew me as half of a couple. My girlfriend and I live together, share most friends and work from the same apartment two days a week. I love our life. I also liked having one room in it where I arrived alone.

I told her that. I thought I was sharing something good.

The following Saturday, she came with me.

She said she had been wanting to exercise more and the group sounded welcoming. I did not object because objecting would have made the reason obvious. She enjoyed it, exchanged numbers with two people and bought the group shirt after her second week.

Now she assumes we will go together. During the run, she drops back to match my pace even when I tell her not to. At coffee, she finishes stories I start. The group has begun inviting us as a unit. The private little life I had for four Saturdays has become another part of our shared one.

Last week, I told her I wanted to attend alone sometimes. She asked whether she had embarrassed me. I said no. She asked whether there was someone in the group I did not want her to meet. I said no again. Then she asked why her presence changed anything if I loved her and she liked the activity too.

I struggled to answer without sounding cruel. The honest answer is that she changes the way I occupy a room. I become aware of whether she is included, whether she is bored and whether a joke needs context. None of that is her fault. It is simply different from being there as myself.

She says couples are supposed to introduce each other to good things. She also points out that I do plenty without her: errands, lunches with coworkers and occasional nights with friends. To her, protecting this specific activity makes it suspicious.

I think the difference is that most of my separate time is practical or inherited. The running group was something I chose because it belonged only to me.

She has every right to run in a public park and remain friends with people she met. I cannot evict her from a hobby. I also resent that my request for one independent space became a question about whether I am hiding something.

Is it reasonable to ask a partner not to join a hobby you introduced them to? If the shared version is already established, how do I reclaim some independence without making her feel rejected by a community she now genuinely enjoys?