Hello Iris: I see this is your first post here on PC. So...

to PsychCentral… from the Skeezyks!

May the time you spend here be of benefit.
I don't know as I am the best member here to be advising you with regard to this. (I'm just a solitary old geezer.)

What strikes me here is that the trauma your friend has experienced is going to take a lot of time & work to heal. Just how long it may take depends, to some extent, on what he's doing to facilitate his healing process.
My personal opinion is that he needs to be actively seeing a grief therapist who can help him, over a period of time, to work through his grief & figure out where he wants to go from here. If he's just "hanging on", so to speak, waiting & hoping that time will heal his wounds, this is (from my perspective) a bad sign. He's going to be hurting for a long time. And if you stay with him, you're going be hurting as well.
On the other hand, from what you wrote, it sounds as though you've somewhat fallen in love with this gentleman.

That being the case, perhaps some individual counseling / therapy for yourself might not be a bad idea either to help you sort out how you feel about this. And along the way, some couples counseling may be appropriate for the two of you as well.
I know that sounds like a lot of "stuff". And it is. But I think if the two of you are going to have a chance to make it as a couple over the long haul, then openly & deliberately taking on what your friend has experienced is going to be vital. Open & honest communication is vital to any successful long-term relationship. If either of you is not prepared to make this kind of commitment then my advice, for what it's worth, is to seriously consider letting the relationship go.
PsychCentral is a great place to get information as well as support for mental health issues. The more you post, & reply to other members’ posts, the more a part of the community you will become.

Plus there are social groups you can join & chat rooms where you’ll be able to connect with other PC members in real time (once your first 5 posts have been reviewed & approved.) Lots of great stuff! So please keep posting!