Just gonna say first I am not the most qualified when it comes to relationships and stuff so I recommend listening to what others have to say as well.
But, I definitely wouldn't say it's too soon. It's something important to you/your life and it could help him in being more understanding in the future and give him an idea of what to expect (by giving you the chance to talk to him abt this). How he responds could also help you understand more about him as a person which is always good.
As for the 'how', I'd recommend just literally just telling him you need to talk to him about something serious/important. Let him know it's nothing concerning your relationship/him and its just something about yourself. You can either pick a 'good' time and start with this and then just start the discussion from there or you guys could arrange a time in advance where neither of you are busy (depends on if you/your bf are the types to need to prepare yourselves in advance for serious topics or if he's likely to worry and want to know right away - in which case you should plan what you want to say before approaching him).
If you're anything like me, you might get tongue tied and struggle to find what to say. If that's true for you, make a few notes (if you're not comfortable reading from notes as you're talking, just go over them beforehand kinda like you're revising something lol). I don't know you or exactly what you want to say beyond making him aware of your situation so i can't really give personalised ideas for what to focus on here. Could also be useful to decide what order you wanna talk about things in so it doesn't get overwhelming or confusing. Start with whichever you feel is the most impactful or prominent (e.g. for me, my autism influences everything in my life including my depression so naturally i'd start with that but I obviously can't tell from this post which issue of yours is most important to you). Cover anything you want to talk about relating to that topic. For example, you could explain how this impacts your behaviour/emotions/thoughts/etc and/or anything he could do to help. Just anything you think you want to tell him. If any of your problems are interwined, you can use one topic to transition naturally into another and make things more concise. (e.g. in my case, after covering how my autism had impacted me in terms of my depression, I would have a way to discuss my depression as a whole without disrupting the conversational flow if that makes sense). Just continue with this until you have gotten through everything you want to discuss.
It's good to give him opportunities to ask questions throughout as you're explaining to ensure he gets a good understanding which will obviously benefit you both. Also, especially when discussing suicidality and self harm, it doesn't hurt to undermine (underexaggerate?) a little for the time being to get a general idea of how he copes with the initial information given to him bc as distressing as it is for the person affected, some people also become really worried/distressed when someone they care about is going through that kind of stuff (more likely if he's had no previous experience with these topics) which is obviously bad for them if they become obsessive over it or anything. By not including too many details, it helps reduce the risk of him becoming too greatly distressed/disturbed
Sorry this is so long, I always had a problem with writing things much longer than needed lol. Not sure if everything makes sense and if any of it will be useful whatsoever, lmk if you want me to clarify anything
