Dating Someone Who Lost a Partner to Suicide

Hi, I hope I’m posting this in the right subreddit.
My boyfriend’s previous girlfriend died by suicide two weeks before he met me. I met him when he was at what seemed like the lowest point in his life, but at the time I thought it was because he smoked weed, drank alcohol frequently, worked 12-hour shifts, and was dealing with family problems. I only found out about his girlfriend’s death later in our relationship.
We’re both quite young. I’ve always tried to support him as much as I could and be understanding of what he was going through. I know that grief can be incredibly difficult, and I’ve tried not to take his grief personally.
At the same time, he has told me many times that he loves me deeply, that he is very much in love with me, and that he wants to marry me and build a future together. I do believe that he loves me and that our relationship is important to him. That’s part of why I feel so conflicted about all of this.
Recently, I came across something he had written about her before we met. It was very dark and showed how devastated he was and how unable he was to accept what had happened. There was one sentence that he repeated three times: “We will return, my love…” Those words really hurt me.
There are already things I struggle with emotionally, especially the fact that only two weeks had passed between her death and him meeting me, and how badly he was doing at the time. He later admitted that during the first two months after her death, he repeatedly thought about suicide himself, although he never attempted it. He did hurt himself a little, though.
Thankfully, things seem to be getting better now. He has stopped using weed and drinking alcohol for a long time, he’s started sleeping a few more hours, and he smiles more. I think he’s doing better.
But I honestly don’t know what I’m supposed to feel about all of this. I love him and I want to support him, but sometimes I feel hurt, insecure, or like I don’t know where I fit into his life and his grief.
How can I communicate with him about this without making him feel guilty for grieving or making things harder for him? What is a healthy way to approach a relationship with someone who lost their previous partner so suddenly and tragically?
I’d really appreciate any advice or perspective from people who have been through something similar.
I don’t want to hurt his feelings and want to be there for him with right words.