Proving adultery is an uphill task

Dear Harold,

I suspect my wife is having an affair(s) following information I received from friends and relatives. I cannot prove my fears, as she plays the perfect wife at home. She, however, has a strange behaviour of walking out of the house to receive phone calls. She also switches off her phone when going to the bathroom. Occasionally, she comes home with flowers, but becomes hostile when I ask her the source. How can I prove her suspected affair(s) and possible adultery?