Sounds like you are definitely in a loving relationship then, you two could maybe talk about love language. The way that you feel loved and the way you show your love to him and visa versa. Either way I think you can figure that out as the foundation of your relationship sounds pretty solid :)

Another tip could be that you can write down what you want to hear from him? That he is looking for someone in his life that he might spend the rest of his life with. Not yet, but let him say it out loud that it's just the marriage part he doesn't like. He probably does see you as a potential life partner, even though you're both not ready to decide that.

And overthinking doesn't have to bad! Makes you a critical thinker, less likely of doing something impulsive. Shows you're smart too.