Confused over a man

One week ago, an ex added me on Facebook. The background is that this is an ex who I haven't spoken to in two years. Though we only dated for a few months, it was extremely intense and the breakup was painful. We had an instant connection to each other. We parted ways with no hope of a future together because (even though neither of us would say it because we knew that it would really end everything) he is Jewish and I am Catholic. He is not religious but I know his Jewish identity is very important to him, as my Catholic identity is to me. Apart from our own personal views, our families have a huge part in that too.

We did stay in touch by email for a few months after, but ceased all contact when it became evident that it would be too easy to hold onto our feelings for each other. At least, this is how it was from my end and how I imagine it to have been on his end, but I can't know for sure.

So when I see his name come up last week, I was in shock and not at all pleased with the reaction in my stomach. That is, lots of emotion, memories, and feelings came flooding back.

I waited a few days to add him and when I did, I sent him a one-liner, making a joke about his profile pic. That was 5 days ago and I haven't heard anything from him. From what I can tell of his profile, he is not in a relationship.

So why has he added me and then not said anything to me? What is up with this? Seeing his pictures again gave me a lot of anxiety this week as it caused a temporary resurgence of feelings for him that I have never had for anyone else. So I was a little scared and even annoyed that he chose to find me now.

I ask myself, should I even be bothering to open up this old wound?