do i tell him?

my ex texted me a few days ago saying he missed me and loved me and we ended up deciding we were going to try again in the future but right now we both have stuff to figure out, he wanted me to stay single and i said okay but then today i kissed someone i’ve been talking to… my ex knows i was talking to them but if me and my ex got back together in the future should this affect our relationship? and should i tell him that we kissed?