Am i overreacting - I think my 26m bf lied over 6 months ago

A half of the year ago I caught my bf messaging his ex. We got into a fight, I wanted to break up, he begged me to stay bla bla bla. After that, he said she messaged him once again but this time he blocked her on messenger (I didn’t ask him to). He swore on it. I didn’t have any reasons to doubt it until now.

I got with my friend I didn’t see for sometime, she was aware of that situation but not that we decided to stay together. She was curious and went on Facebook and saw that they are still friends on Facebook. She told me that when you block someone, that person automatically stops being your friend on Facebook. I was not aware of it, but checked it; and it’s true. I didn’t think about it anymore until now.

Should I ask him about it after 6 months, or should I let it go? I am thinking about it since I learnt.

Am I overthinking?