Whether or not it’s “okay” to swallow semen depends on whether or not you’re okay with it. There’s nothing unhealthy, wrong, or dirty about swallowing semen, as long as you’re comfortable with it.
It’s not possible to get pregnant from oral sex, whether or not you swallow. (That’s because your mouth isn’t connected to your reproductive organs.) But having unprotected oral sex (again, whether or not you swallow) can put both partners at risk for a number of STDs, including gonorrhea, hepatitis B, herpes, and humanpapilloma virus (HPV). For safer oral sex, use a condom to cover the penis, or a dental dam to cover the vulva.