Bi and gay

Please do not bash me. I am very curious. Someone just told me they were bisexual and gay. I thought it was either bisexual or gay. Please do not think I'm being mean. I am honestly curious. Is it possible to be both? I feel bad for this person because they said they are gay and that they use women as a cover up. And I am just trying to understand him more. I've been told it's not possible to be both, while I have also been told that's it is possible. I'm so confused. Is it possible he's just saying this to avoid being attacked by others who may not agree with him instead of being open about liking men only? I did look up it up on Google, and one website did say they could be gay, bi, lesbian, or asexual ECT. Can't remember exactly what it said. But this is the jist. Please educate me on this. I'm trying to understand better, and help him if I can.