It doesn't make a whole lot of sense to ask for help stating you have no idea what you are doing, and saying how you rage quit games and then go around offering advise like you know what you are talking about.
I play a blood dk, and I can tell you - Yes, they have absurd survivability in PvP. Their damage is maybe 75% of a DPS spec. Man, you give me 3 opposing dps players and I will smash them into the ground. Throw a healer in there, not so much. However, to kill a blood DK you must do 1 of two things:
1. Do so much damage that you out damage his healing. Not going to happen with less than multiple people.
2. Prevent him from healing. Viable ways of doing this are: Disarming (Prevents a lot of healing because he can't Death Strike). Silencing (Prevents all healing cooldowns via Vampiric Blood, Rune Tap, Death Pact, Conversion, Empower Rune Weapon). Kiting (Prevents Death Strikes so he can't heal). Stunning (Can't do anything, duh).
As a Ret Paladin on your own, you should honestly just give up unless the blood dk is both stupid and undergeared, because you won't win unfortunately. Bring some friends or ignore the DK. The control a DK brings is limited entirely to his talents - A choice between a slow via Frost Fever + Roots on Chains of ice, or reducing the cooldown of our one minute silence to 30 seconds and turning it into a stun, as well as a choice between mass death grip, mass 5 second build up stun, or extra pvp trinket zone. Plus Death Grip. A blood DK does not have enough CC to bother killing either, so just CC them if you really care that much, or don't hit them.