I'm concerned that you don't seem to have spoken to a L?
In the U.S., all the debt he's racking up with his GF would be joint debt.
Time to grow up. This is not the man for you. He is not your lover, your partner, or your friend. He is not even minimally decent.
(1) Get out of the house ASAP, take anything you might want, you can always return stuff later, much harder to get it later.
(2) Get a L.
(3) Get tested for STDs.
(4) Get H off of your credit cards, insurance, cell phone account, everything.
(5) Quit blaming his GF. She is still pretty much a child, a very damaged hurting child who is acting out and is being used by H and plenty of other people in her life. The problem between you and your H is your H, not her. Forget her or find compassion for her. But quit obsessing about her and blaming her. She is a very damaged child engaged in a lot of self-harm. Very sad. And, while your at it, extend that compassion to yourself. He probably misused the teenager you were when you met in the same way.
(6) Stop interacting with H except for business matters, and try to let L handle those. H is not good for you. You actually seem a bit stuck in your very young adulthood a bit, probably because your VERY stuck H kept you there. When you started to mature some, he started looking for another child. Don't let him stop you from becoming a strong, happy, independent, passionate, interesting woman.
