I (34F)found a girl on his snapchat askin my bf (38M) to send her videos of him fucking. ..

So I havent quite yet thought about how I am going to confort the conversation with what I ended up seeing... not sure how or when but I had signed outta my snapchat account and realized there was another account on my phone & sure enough it was my bf. WHICH NOW I can recall him signing in using my phone like 2 years ago when he was waiting he's new phone in the mail.. so anyways ofcourse I got curious, I didnt think it was going to allow me to sign in since it had been so log ago he had used my phone to access the his account. Then BAM ! I CLICKED IT AND was on it.. i immediately saw the top threads of chats of some girls in whom I dont know n im sure he doesn't know em as well they could be outta state ,.. anyways I clicked on the chat and seen he had replied to some story's she had posted earlier the day & him ❤️ the pictures .. she then replied back 2 hours later asking him "send me a video of you fucking"... He then replies bk several hours later ,.. and he sends this girl a video a small video of me n him having sex its like a 12 sec video but the audacity of him acting as if he has no self control its beyond flabbergasted that he could send this random girl a video of me n him having sex.. like first of all I wanna know WHO TF is she to you !?? N Why the fuck do you feel entitled to fulfill her requests to go as far of sending her videos of us having sex .. .. there was another either Pic or video sent but it was red black out just saying delivered.. obviously this only appears like this when one uses the self camera that's an option to take a Picture or video and sending it for a time managed glimpse so.. im now im wondering what else did he send to her that now I can't see. This happen today around 10am and til this moment she still hasn't even opened the message nor has he sent anymore pictures or videos...Am I overreacting or should I just flat out ask him. We've been 5 yrs together and we live together for 3 almost 4 years .. any guidance or advice anyone please ?