Why do I keep committing suicide?

The maximum leech duration is 5 seconds, but only if you're dealing enough damage to reach that amount. It's possible you simply don't deal enough damage and the leech only lasts maybe 2 seconds instead.

Is it for sure bleed degens that kill you? Maybe there are chaos or other ground effects instead, especially if deaths are happening around metamorphs. Having maximum resists is pretty standard for end game and you are just a bit short.

Check your character sheet and/or gear to see if you have any added chaos damage modifiers. I think that Poison may be instant killing you because resistances for this type of damage is typically negative for the average player. Physical damage and Chaos damage has a chance to inflict Poison, and since it bypasses energy shield. Given flicker strikes innate mechanic to be everywhere at once, you're probably applying way more Poison stacks to yourself than you can mitigate.