Hi,
1. Seek legal advice
2. Apply for a court order and apply for full custody, with only supervised visits with your children (ie a third party will be present to observe and make sure your kids are safe when with him).
3. Apply for a domestic violence order (or the equivalent where you live). If he breaches it, call the cops so he’s arrested.
4. Call the cops every single time he shows up and your house/place of work etc. now: This helps build an official record of how he’s trying to harass, intimidate and stalk you.
5. I’d consider moving out of the area totally with your kids. He can’t harass you if he doesn’t know where you are.
6. Let all calls from him go to voicemail. Keep them as evidence of any abusive language/threats he makes. Sane with text messages-take screenshots of them.

It’s not about you not being ‘good enough,’ it’s about him and a perverted choice he made to sexually assaulted/rape a minor. That’s entirely on HIM, not you. Not anything you’ve done or not done. You haven’t ‘failed’ as an intimate partner. He’s a grown adult who has made a conscious choice to act inappropriately. That’s on HIM, not you. That’s HIS personality, not yours.

Try to get some trauma-based counselling for you and your children. Try to get well enough to get a job , then MOVE and cut him off. Don’t correspond directly with him - keep everything in writing. Warn the school not to let your Chikdrrn go home with him once there’s a domestic violence order in place. Show them a photo of him and have them keep it on record, so they know your Chikdren are not to leave with him.

Don’t let this pig of a man ruin your future life. Don’t communicate with his family. And please don’t be a sitting duck copping abuse from him and his family. As hard as it seems-you need to find some inner strength and start to be proactive in getting away from him and then. Physically (by relocating), financially (by getting a job), emotionally (by seeing a counsellor/therapist), legally (parenting order/divorce/domestic violence order).