Assuming you're immigrant with conditional GC...
0) Make sure you and your child is safe.
Make copies of all important documents and evidence of relationship. Store originals with friends / safe deposit box at bank or other safe place. Store copies at friend's and / or in the cloud.
1) Decide whether you want to continue the marriage with the spouse. Can these problems be realistically solved? Do NOT factor in immigration at all. It's on a separate track, though somewhat related, you can remove conditions after getting divorced. You don't have to rely on US citizen spouse.
2) If you decide to divorce, don't wait. In some states it's a lengthy process. Speak to family lawyer and get to know the process.
3) If divorce is fast, you can convert I-751 to divorce waiver after divorce. If not, then you may need to consult with immigration lawyer about best timing for converting petition.