Yes he can. He goes and has sex with a woman, and they make babies.
Maybe it happened before he realised he was gay. Maybe he was really drunk. Maybe she was a surrogate for his child. Maybe he was a donor for her child, because she wanted a suitable male partner without the relationship. All of these things happen.
If - as you seem to be - you are talking about homosexuality as a behaviour in species that do not have self determination, or the ability to artificially assist conception and birth, then it is possible that there is some evidence of homosexuality being selected against as most homosexual behaviour in animals tends to be a component of promiscuous bisexuality.