I am self-employed. My spouse as a full-time job with employer-provided health insurance. I pay $70/month to be added to my spouse's health insurance. Can I deduct my costs of $70/mo on my Schedule C?

it depends; You can't deduct the costs of health insurance if your spouse was eligible to participate in a subsidized group health plan through an employer This might be the case if your spouse becomes employed and is eligible for coverage under a group plan