I think this is a horrible weekend for you and I can imagine you might feel a bit disconnected from events, almost as a survival mechanism. Make sure you grieve properly though, citydoll and therefore I'd echo PP's advice about therapy, but if you do go down that route again, choose a good practitioner and screen carefully, because there are some awful myths about infidelity peddled by society at large - and therefore therapists.
At times, people in your shoes can feel worse afterwards, not better.
You might find it especially helpful to join the thread where the main contributors affectionately call themselves "dumplings". In reality, they are inspiring, brave, wonderful women who are all at different stages of loss and recovery.
I would echo what has been said about challenging that inner dialogue that you are old and beyond a new relationship. My friends range from 35-60 in ages and that has not been my experience at all. However, if you have been part of a couple relationship for 37 years, I think one of the exciting things about that is the opportunity to be selfish and self-contained, if you are going to live alone.
One of the best pieces of advice a friend in a similar situation to you was given, was to have a default position of "yes" when invited out, but not as a means of total avoidance from the grief. The donor of this advice had spent months turning up to every event as a means of keeping busy, until a song on the radio caused her to crash spectacularly.
Wise words, that my friend learned from, to which she would add, keep a journal. This really helped her to track progress and her passage through the bereavement cycle, until she reached acceptance.