How exactly did you file your 2018 and 2019 returns?
Where did/does your spouse live?
Does your spouse have income from US sources?
You can never claim a spouse as a dependent. However, you may be able to file a joint return, which has lower tax rates than married filing separately. But there are some trade-offs to consider. If you filed as single, you definitely must amend your returns to file either as married filing separately or married jointly.
