<human>: Can you give me a shortened version of the text?

So I found out today my good friend Brittany[29F] who I have/had (I don't know anymore) feelings for was hooking up with her best friend[28F] Jen's ex Mike[28M] for at least a year behind Jen's back. All 3 of them have been best friends for years and this is a world changing discovery for me. Brittany and Mike for the most part just seemed like best friends, but looking back there are obvious signs that this was happening that I missed. Mike apparently called things off in a moment of clarity somewhat recently when he realized what he's been doing. I'm really good friends with all 3 of them and I know it would tear Jen apart to know that this happened. Since I've known all 3 of them Jen occasionally gets jealous when Mike starts to see other girls, and the fact that her best friend was hooking up with him would probably break their friendship apart. I realize my feelings for Brittany may complicate matters but I'm really torn on how to proceed. Let them continue to act like nothings happened between them? or let Jen know because this is something that feels extremely dirty and wrong.

This is also leading me to question my feelings for Brittany because I thought I knew her, and this is something so contradictory to the person I thought I knew that I don't know how to feel anymore.
<bot>: Girl I like was hooking up with her best friends ex for at least a year behind her back. Tell her best friend or just ignore it?