What do I do?!

Been seeing this guy for over a year, in march we agreed to leave things and didn't speak for a month. In the gap I slept with my friend who works for him - we started speaking again and have been seeing him since but recently he's started questioning me so yesterday I was truthful and told him I slept with someone else. He's been very calm but I have a gut feeling this is the end😩 I just don't know what to do! Thank you for reading this x