Help!

I need someone to talk to. A quick little bit of info about us, I've been with my SO for almost 5 years, he is 22 and we have two kids 18 months & 2 months together. He has a great job and the plan was for me to stay home with the boys. He has a job that requires travel, well he left two days ago for a week in California. We've had our problems before and always tried to work through it and I'm not saying im perfect but most of the problems started with him (trying to text some other woman) & lying over and over and over its so crazy. Like he cant stop but gives this huge speech about how he's so shitty and he'll change. Well he took his work phone but left his personal phone at home. Not a huge deal I put it on the fridge until he gets back, but then he texts me and says ok I need you to get on my phone because I need this code and I sent him the code. I saw one message from him that asked his friend "are we still getting coke saturday?" Now this has happened before and he tried to tell me they were talking about cartridges or something for vaping? Like a flavor? Idk im not super familiar with all that but this was definitely not about that and now im second guessing if the other time was about actual cocaine or a flavor for vaping. He's defended cocaine before when we had a conversation about what was bad. He said its something you can do then never think about it again. He said its fun if you do it right but added "thats whats i heard" he plays music with his friends. They have a little band and that text was from a night they were supposed to have a gig somewhere. Am I wrong ? should I just let this go ? Or leave? He's going to be pissed if he knows I saw his messages and he'll act out if I accuse him of doing drugs but this isnt what I want for my kids at all. I dont want that around them, I want them to have such a good life and if he really was talking about cocaine then that would explain a lot. He'd lash out on me for no reason. One day he was talking and apparently thought I wasnt listening so he pushed me against the fridge and yelled in my face. I thought things were getting better. Im so depressed right now. Its so much dealing with a toodler and newborn by myself and on top of that I'm trying to decide whether I should pack up and leave or not. ☹