The most important thing for you to understand is that he will never get over it. In time, he will likely learn to live with the loss. I hear your concern for him, as you are obviously a caring friend. You may want to consider your own expectations about what you think his grief should look like. It is a hard thing to understand if you haven't been through it, and it can be even harder to know how to begin to help; there is so much pain. In our culture, we often aren't taught how to honor and hold space for our own and others' pain. Yet, doing this is so powerful and healing. You can absolutely suggest therapy to him, but not because he's "not over it," rather, because you care about him and think having someone to talk to might be helpful. Please check out these other resources to help you be even more of a resource for him: https://www.refugeingrief.com/2018/07/19/help-a-friend-video/
Keep being a good friend.