“What happens if you swallow semen? Is that ok?”
It depends on whether or not you are okay with it. There’s nothing unhealthy, wrong, or dirty about swallowing semen, as long as you’re comfortable with it.
FYI: It’s not possible to get pregnant from oral sex, whether or not you swallow. But having unprotected oral sex can put both partners at risk for a number of STIs, including gonorrhea, hepatitis B, herpes, and HPV. For safer oral sex, use a condom to cover the penis, or a dental dam to cover the vulva.