I am sad because I feel that I have no intrinsic value. I have spent my life pinning happiness to things that are often only short term measures to keep unhappiness away.
This says to me that you can stand to strengthen yourself. You can use this separation to good ends. If you are looking for him to save you, that is not a good sign. If you emerge from this separation feeling powerful and strong and independent, and YET, you still want him, then you will be in a position to be present for him, long term. If you are weak and needy and go back to him in that mindset, then yes, you will be susceptible to another affair.
The separation stinks and is not what you signed up for. I get it. but could there be something you could learn? Could you improve yourself during this time? is it an opportunity for you?