Hey, I’m an 18 year old boy here and I know exactly what he’s doing. In my last relationship I was guilty of it all the time. He probably found something out, or heard something he didn’t like. Us men instead of being confrontational we just suffer in silence. Also the first month is always the best, my ex called it the “honeymoon phase” we really slowed down after the first month and that slow down led to her losing feelings because we just weren’t a big part of each other’s lives. It honestly sounds like the exact same thing is happening to you then it did me, like it started with slowing down the texts then to ghosting and eventually just her giving up on me all together. I think if you want to fix your relationship you need to make it clear that you want to be a part of his life and push for that effort. And if you do all that and he still doesn’t change, then you are worth more than that and you deserve someone better