Is he getting treatment? Is there other ways he can support you that don’t require you talking about it? Cause otherwise that is a bit selfish of him tbh (am I say this as someone with OCD & have had those kind of themes). I know how debilitating it can be but as your bf he should still be finding other ways to show he cares and that you’re not alone in it.
Idk if his ocd was the same as mine, I had OCD where I had a little bit of every type until I went into remission. But I understand both sides, OCD can really latch onto anything he might obsess over you getting an infection from SH or dying and it might take up a lot of his time. But also I understand you needing support and an outlet. A good compromise would be to name feelings and emotions in other ways as opposed to “I’m feeling suicidal” or “I want to SH”. Instead you can say:
He’s not getting treatment. He did say that he could still support my with my depression, but he doesn’t seem to understand. I’ve tried telling him, but when he says all families have problems, it feels like he’s invalidating my struggles and PTSD. Like, no, they didn’t just “make mistakes”.