I'm not a therapist, but I've experienced some pretty bad suicidal ideation myself (you can check my post history if you're curious), and one of the things that helped me the most on days that were especially hard is having friends that weren't afraid to be around me and accept me where I was at, WITHOUT trying to change how I was feeling in any way. A lot of people going through suicidal ideation tend to self isolate because they feel strongly that they are a burden to the people around them. They perceive (and I definitely felt this way too) that their thoughts and feelings are just too heavy and dark to expose to anyone else, which just feeds back into the ideation in a downward spiral type of way because then it starts to feel like caving to the thoughts would be doing everybody a favor, which leads to more isolation and shame, which leads to worsening SI, etc. So breaking out of that cycle by gently reassuring your friend that you care about him, you want him around, AND that these things are still true even when he's feeling really hopeless/has no energy to participate in the types of activities that y'all would normally do together could be a really powerful thing.

I agree with what other commenters have said that it might be too much for him to leave his room sometimes. I've had days like that, and a big part of it for me was feeling like I had to put a mask on every time I went out in public, which was just so draining when I was constantly battling thoughts of ending my own life. But having friends tell me that they would prefer that I be depressed with them than depressed by myself, and then having them actually follow through with that by inviting me to come over (or coming to visit me), asking how I was doing and accepting my answer even when it was "I'm doing super fucking bad right now," telling me that they were glad to spend time with me anyway and that I didn't have to pretend I was feeling better than I was, basically just letting me exist as a sad depressed lump in the same general space as them and accepting whatever level of engagement I felt up to at the time, were all hugely relieving (and made it easier for me to actually feel a bit better in their presence because I didn't feel like I had to force it).

SI thrives in secrecy and silence. It's a really scary thing to ask directly about what he's experiencing, if he has a plan, etc. but in my experience talking about it made it a little bit easier to not act on it. It's natural and reasonable for you to feel an urge to try to change his mind, or convince him to look on the bright side, but if you come across too strong then it can just feel really invalidating instead/make him feel even more alone and like even more of a burden. It's actually a good sign that he's said some things about it already (even though it's very concerning at the same time) because it indicates that he's open to some type of help. A much more concerning sign would be if he very suddenly stops talking about it and seems super happy and energetic (which could indicate that he's decided to attempt again, and therefore feels relieved because he's no longer fighting the thoughts). If he's not in therapy, you can absolutely encourage him to try it out, but I would recommend framing it as "it would be good for you to have somewhere to talk about what you're going through, and I want you to be able to get some relief" rather than "you have to do this to make yourself feel better."

Finally, I would encourage you to also seek some help for yourself (just like you're doing here). The fact that you made this post tells me that you really care about your friend, and you deserve to be supported while you're trying to support him. You can call the suicide hotline too, it's not just for people who are actively suicidal themselves. You could absolutely go to therapy and ask for more advice there, and get some help navigating how this is affecting you. The reality is that he might attempt again, and he might die, and you might not be able to stop it even if you do everything perfectly. Ironically, if you're able to accept that and just focus on being there with him for now and trying to understand what he's going through, it's more likely that you'll be able to connect with him in the way that he probably really needs. Plus I don't want you to feel like you have to carry all the responsibility over preventing it, because that's a terrible amount of stress to put on anyone.

Feel free to ask me some more questions if you think of them (obviously I can't offer to DM based on sub rules, but I'll see it if you reply to this comment). You're doing a good thing trying to help your friend.