It Wasn't Just A Workout Session

I'm a personal trainer and have been for about three years now. I work with people to help them reach their fitness goals and feel better about themselves. But something happened last week that made me question everything. She's one of my regular clients, a married woman in her mid-thirties named Lisa. We've known each other long enough that she trusts me completely, both as a trainer and someone who understands what it means to push boundaries. It started with her coming late because her kids had the flu; I let her use my personal room to freshen up before working out. One day after a session, while we were cooling down on mats, there was this awkward silence where both of us seemed lost in thoughts. She confessed she wasn't feeling close enough to her husband lately and asked if it was okay to vent about her marriage problems with me. I felt like an idiot for agreeing but wanted to be supportive. Over the next few weeks, our talks got more personal; we shared some intimate details of our lives without crossing the line into something inappropriate. Until that one Thursday when she suggested we should try a new approach to fitness. She had booked this private room at another gym for an exclusive workout session. It turned out there was someone else in the room, Mike, another trainer from her regular group sessions. I didn't know what to think but felt like it could be beneficial for Lisa's training. But then things got out of hand. We ended up doing more than just working out together... I told myself it was only a one-time thing to support my client and that we'd go back to normal afterwards. It's been weeks since, and I feel so conflicted about it, ashamed and confused. I didn't want to betray Lisa or harm anyone but somehow found myself in the middle of something I never thought I would be part of. I can barely admit this to myself, let alone anyone else.