situationship gotten complicated

okay so basically i’ve been seeing this guy since the summer and we recently had sex for the first time, then i found out that one of my friends was trying to hookup with him behind my back. here’s the thing, we are not together and we always tell each other about who else we may be seeing for the purpose of transparency.. but him telling me that my friend messaged him for sex made me uncharacteristically angry and jealous. please comment thoughts on this because i’m unsure how to handle this situation.