Hi Hanging,
Congratulations on the new opportunity!
Like tryingsome mentioned, for a person with low self worth, the idea of someone else succeeding can be hard to deal with. It could mean change, it could mean you will realize that you're a wonderful person, and you might leave your BPD loved one behind. It's something happening to you, not your partner, they could feel left out. Or sad that it isn't happening to them.
He is not necessarily trying to sabotage your success. He is trying to survive the anxiety it produces in him.
When he creates tension over your opportunities, how do you respond to him?