is he “cheating?” is this justified to get mad over?

so... my boyfriend of a few months and i just came to the mutual agreement yesterday that we are taking week long break, but that we agreed to stay friends in the mean time. all was fine and good, and we texted regularly throughout the day.

at about midnight i texted him “what did you do today?” he responded he played basketball. his answer seemed really short and he didn’t attempt to keep the conversation going, so i said “oh that’s cool! did you do anything else?” to which he replied “nope”

he then stopped responding, so i looked on snapchat maps (i know, probably an unhealthy habit!) to see that he was active right now, and at his “GIRL BEST FRIEND”’s HOUSE? and just so you get the whole picture, this girl has liked him for months, and has outwardly expressed her dislike for me because of the fact that i was dating my boyfriend and she wanted him

he left to go to the girls house at midnight, and was active on snapchat until 4 AM which is when i assume he fell asleep there. keep in mind he has never slept over at his girl best friends house, this is the first time that i am aware of it.

the whole time he hasn’t responded to my texts, and I even made a point to say, “okay well goodnight then! :)” to which he still did not respond or acknowledge! but i know he was on his phone because it said he was active on snapchat :(

is it reasonable to be mad at this, and to be suspicious of this situation? we JUST decided to take a break today, and he decides to sleep over at the girls house? and am i even justified to get mad because technically, we are “on a break” so it’s not cheating if he hooks up with another girl?

my heart hurts and i just want to know whether or not you guys think this is a valid enough issue to call him out on :( please let me know