Hi Herodias,
That must have been so awful for you. I can't imagine how I'd feel if it were me. You were very self controlled to not say or do anything and I think that's something you should be proud of. Your sister is probably right in that showing your feelings to this woman would likely be taken as a sign of weakness. In time when you are feeling stronger, maybe you will be able to walk into her workplace and swish past her with your head held high. You are not the person who ought to be feeling bad if your husband was cheating on you. Try to remember that. It sounds to me like you've been through enough already and it's no wonder it is taking it's toll to have such a nasty surprise. Be kind to yourself now and do whatever makes you feel good. For me sometimes that means a toffee cream meringue

That moment of bliss helps! Good job I go to the gym regularly
Healing takes time. Just look after yourself and as you said, steer clear of that individual if it's damaging to that healing. For now at least. Great to hear you have a supportive sister. Those relationships are important when we go through life's low points, aren't they? Perhaps there is something the two of you could do together just to take your mind off things at present.
Love and light x