It might help to talk it out with him, and make sure you're on the same page. You can see what works for you! Maybe you'd like to write down what you have to say, and either give it to him to read or read it aloud to him. It generally helps to keep a clear, level head and know what you want to say.
Talk to him; set a proper time, find a conducive place, communicate beforehand that it's very important.
In the meantime, avoid nagging when you're worried and tempted to do so; if you feel as if you can't help but nag or worry, it means you need to seek support or refuel, but it does not have to come from him.
Sometimes people need a little space or time to themselves, this doesn't mean he doesn't care about you it just may mean he is overwhelmed with the fact he has been in a committed relationship for over a year. I'm sure that with time and effective communicate between you both you will sort it out. Make sure to talk to him about it though so he doesn't feel alone.
a Zelda similar experience, and I wouldn't immediately jump to the conclusion that it is something because of you. And my personal experience and ended up being something that had nothing to do with me, and I nearly derailed my self-esteem because of things I assumed. Do not assume it's because of you, he may be going through something personal. What I would do is I would approach him and in a way that is not prying, I guess you guys speak about something that he may be going on personally, maybe an internal problem that he's uncomfortable sharing. Chances are it's something he is going through maybe feeling unworthy, maybe he as some other issue going on and he's waiting for you to ask him about it. Just let him know that you're there for him and available when he wants to speak IF it is true... let him know that you will accept whatever it is lovingly. Perhaps engage in a serious thoughtful conversation with yourself beforehand. But only let him know that you'll be there post-revelation if honestly youve decided that you will be. If not I would not mention it, but I would nonetheless, sit down with an open mind let him know you're feeling rejected. Really, he may not know that he's making you feel that way. It could ruin a very great relationship by holding things that I'm assuming you know exactly what he's thinking because we never know exactly what anyone is truly thinking.