A group run by my advisor's former student keeps scooping my work. Is my advisor sabotaging me?
Something is clearly wrong here. If your supervisor is not alarmed, talk to another senior person and make pretty damn sure your supervisor is correct not to be alarmed. There are many people you can ask: your thesis committee, your head of department, a trusted faculty member, someone from the School of Graduate Studies, and so on.
Ask to speak in confidence - something is clearly wrong, and that something could be your supervisor.