I dated the same guy all throughout high school (yes, all of high school-- as a summary: he's a year older and lived about 20 minutes away from me, it was pretty serious) and the relationship lasted through November of my freshman year in college. He broke up with me but it was pretty amicable, and we stayed in contact online but didn't see each other in person for about nine months. When we did see each other, he told me he still wasn't over me (which I'd guessed from other things he'd said) but took it well when I told him I didn't feel the same way.
It's now about a year and a half since we broke up (so about 6 months from him saying he wasn't over me) and I think he's over me. We still talk occasionally, and I'm definitely open to being friends with him, he's a super nice and cool guy. However, when I think we're just having a casual conversation he'll often drop really big/tough subjects (for example, when I ask how he's doing as a conversation starter he responded that he was hospitalized, I believe for mental health concerns). This has happened about three times in the past few months, and I have no idea how to respond. I don't feel that we're close enough for him to talk about these things with me, but I don't want to make it seem like I don't care. Ideally, I'd like to remain friends with him.
Usually what I've done in these situations is ignore the message and wait for him to pick the conversation back up, but this seems really rude to me. So, my question is, How can I ask my ex to stop sharing information that I feel is too personal for our current relationship without ending our friendship?
Edit: I'm pretty sure he has other, closer friends (but not sure). He's still in contact with our mutual friends from high school and he's got a club at his college that he really connects with. He might still not be over me, but it hasn't been as overt as it was before the summer. I've asked our mutual friends about it (probably not the best/most honest move, I'll admit) and they say he's over me, but it's possible they're just saying this to make me feel better.
Note: this is my first asked question, I'm sure I've made mistakes so please let me know if there's anything I should add/change/remove :) Thanks!!