So, you’re 18 and he’s 22 and you’ve been together for about six months with one failed attempt at sex and no other tries. You found gay porn on his phone, but didn’t tell him about it, and he’s told you that in the past he thought he might be gay, but decided he wasn’t.
First, I think you need to be honest with him and tell him that you found the gay porn on his phone. Because it bothers you, whether it was gay or straight porn, talking about it is something that any couple (gay, straight or anything else) would do because honesty is important in any healthy relationship. So talk to him about what you found and why you didn’t talk to him about it right away. This may open up the conversation about your concerns that he is gay and not comfortable with admitting it to himself as well as others.
Second, don’t move in with him. Six months is not enough time to know someone enough to make an important decision about moving in together. In general, I advise that you date someone for three months, after which you decide if you want to continue dating them, and if you do, for six months to decide if you want to be monogamous. I don’t think you have the goods to be monogamous with someone you have so many questions about.
So talk to him about the porn and his possibly being gay, and if after doing so, you want to continue to date him, you should do so, mindfully.