I think my wife is cheating

Married for 8 year. We have had plenty of **** periods in our marriage. Ups and downs. I battled drug addiction for years. She has back problems. What I am getting at it that our relationship has been stretched thin. Long periods of no love and no sex. In September was a fight month. Not good. At the end of the month I go on a work trip. Now with my wife’s bad back she’s been trying to find a massage therapist that’s worth a damn and had found one about 7-9
Months ago. He was a perfect fit. Just a half hour and he worked her in a special schedule so she didn’t have to miss work. As the months go by her sessions start getting longer. It was 5, then 5:30. 6. 630! Until one week she came home at 7. I asked about it and she told me a story about how he’s practicing for some test and she’s the Ginny pig. This was odd but I let it go cause she was happy. Around this time I noticed she’d lost weight (10-15 pounds) and she said she’d been going to the gym on lunch. Odd thing to not mention before to me but I let it go. Fast forward back to my work trip. He session day comes around mysteriously he phone dies sometime around 3 I’d guess. I don’t hear from her until 11:45 as she’s driving home. I was so tired/stressed that I don’t even remember what she said but it was along the lines of they smoked up and she had to
Much and “passed out for an hour or two” we never talked about that day sense. Now I get home a few days later and she’s all lovey and caring but that only lasted a week before a few day meltdown. Now she’s questioning if she wants children or not.
I don’t know what to do. I know I need to talk to her about it all but if she’s cheating I want to catch her red handed