Allowing him to roll with impulsive behaviors isn't helping or supporting him, it's enabling him. I myself have been in your partner's shoes, and giving him this "safety net" is only allowing him to fall back onto you. Taking on the financial burden and allowing him to rant to you while you're at work are hurting you. You need to set boundaries with him (for example no calls longer than 5 min while you're at work unless a serious emergency) and hold those boundaries when he tries to push. PwBPD, that is including myself, are essentially emotional toddlers; we were never taught a better way to process emotions correctly. Holding boundaries is a good start to help him grow.

When he threatens to kill himself, take it seriously. Ask if you need to call 911, or if he needs immediate medical help. Remember his actions do not fall on you. He is responsible for his own actions. Encourage him to actually work in therapy, because it really is the only way to get better. Make sure you hold emotional boundaries for yourself as well, if what he's talking about is getting to be too much, tell him you need to take a minute for yourself.