with a person before but he slept with his pervious girlfriend. They were in a monogamous relationship and it has been more then two and a half years since they slept together. My question is; is there any STDs that can be dormant in him for so long but still infect me if we don't use condoms
After 2 and a half years, the only stds I would be concerned with him not knowing by now are syphilis and herpes. I don't know what country you are in, but syphilis is uncommon in most developed countries.
Both are easily tested for. For herpes, have his doctor do an IgG type specific herpes blood test. You should also have the test done. Over half of the population has oral hsv1. If you've ever had a cold sore, you have hsv1. That can be transmitted to someone's genitals via oral sex