Trying have another baby

My partner and I have tried have another baby but struggle long times no successful. I've been see my GP to test my ovulation and said my ovulation fine. We assume problem is my partner on medication (Meth) which mean affected sperms 😕. My partner tried reduced his meth every few months taking slowly progress. I feel low and sad Coz I don't want miss chance get 2nd child I always want for my 1st child have a little sister or brother long time. Do anyone who have same that situation- meth do affect or not?