HELP! I SUSPECT MY MUM IS HAVING AN AFFAIR OUTSIDE!

Hi all

My sister (now in confinement) and i suspect that our mum (in late 60s) is having an affair outside. Some background to justify our suspicion:

a) Our dad is working on very regular hours. Each time he is out at work, my mum would talk to this "old man" on the phone for long periods over several phone calls. We have calls details records from telco so would know that she has been calling this number. We called back and it was answered by an old man each time. Whenever we asked her why the phone engaged for so long so would claim talking to my aunt else she just give a filmsy excuse. Apparently we found that this man lives in a studio apartment for senior citizens - he is either single or widowed as we never heard his wife pick up the call.

b) She goes out very often and each time claiming that with her RC friends for talks, activities.

c) When my sis was heavy with a child and about due she requested my mum to get her lunch as she couldn walk. My mum came to her place at 9am with overnight food and claimed that she has activities at 11am so cant buy lunch for her. If she loves us, she would have put is in priority right? why put the "activities" as 1st priority and sent cold overnight food to my sister? where cant she just for that day skip the "activities" and be with my sister who was about to give birth anytime? why cant she prepare fresh food for my sis ? why ? because she wants to rush to her activities and had no time to prepare fresh food.

d) we found it very dubious as each time she is not consistent with her reply - an indication she is telling a lie.

PLEASE advise if i should just confront her direct ? Help ! Btw, both my sister and i are married and not staying with her. She stays with my dad.