What did I do

Last night I found out my husband cheated on me 6 weeks ago. its the most devastating thing I have had to deal with this year. It doesn't help that it happened after I gave birth to his second child and in recovery from having a C-section. the worse part of it all it was with someone we both know and he claims he doesn't know why he did it. I don't even know what to do feel or think at the moment.