Asalaamu alaikum (peace be upon you) sister farah.
What you did in the past wasn't your fault, and what happened after - it was wrong, and alhamdulillah you realised that.. love is tough, and sometimes its hard to move on.
To take things in steps, i think we'll give you some tips;
Allaah's Messenger, Muhammad (peace be upon him) said:
“Fear the dua (supplication) of he who has been wronged, for verily it ascends to the skies faster than the rays of light.”
(Recorded in Al-Haakim, Saheeh).
In other similar narrations, it is mentioned that Allaah will respond to the prayer, even if it takes a little while. Since Allaah is testing all of us, whether it's through the good and the bad.
Also, the Messenger of Allaah (peace be upon him) said:
So all these trials you are going through now, insha Allaah they are a source of forgiveness for your past wrongdoings.
So no.1 - make alot prayers to Allaah to make an easy and suitable way out for you from the situation and difficulty you are facing. This is really important since it's Allaah Alone who can provide a way out for you.
No.2. If you feel that the ex guy is causing too much trouble, you have the right to call the police. Since he doesn't have a right to come into your property without your or your mothers permission. He doesn't have a right to harm you guys at all, especially when the past relationship doesn't even exist anymore.
It may be that Allaah provides a way out for you before this though, so maybe this can be used as a last resort if it's required.
No.3. Try to find practising sisters who you can get involved with, maybe you can discuss the situation with them and they can help you in some way.
About the new person, i think it is better that you try to stay out of this haraam relationship. Or maybe get married? I really don't know, but consulting a scholar would be really important about your situation.
Here's a good link where you can post the question:
I'm sorry for not being too much help, but remember to continuously place your trust in Allaah.
We will also keep you in our prayers sister.
And Allaah knows best.