Advice? TW - drugs

I’ve been on and off with my high school sweetheart for 6 years now. We have two kids together who are 16 months and 6 months. We broke up from August until February and started to rekindle our relationship. During the time apart he started doing hard drugs, mainly meth. He got out of that and I didn’t think anything of it. The past week he was with his brother and I found out he relapsed. He came back home two days ago and swears he’s done doing it, but as someone who grew up around active addicts I know he’s going to stay clean until the urge comes again. I’m trying to help him and be here for him, but it’s destroying my mental health. I don’t know what to do. I want to try to fix my family because I do love him but I can only take so much. Drugs have stole the person I’ve loved for a long time and I’m just lost and don’t know what to do or how much more I can take.. 😕