Due to my past "behavior" my current partner is considering leaving as she does not trust me and thinks I continue to lie to her.

After we got back together after a period of time apart where I met a few other woman in between, she asked me about previous partners and I said I was single.
What I didn't say was that I had a woman stay with me for 3 months until she went back to her home country and I felt it wasn't going to work.
What happened after was that I tried to conceal my past as I knew it would be difficult to explain my decisions and choices. After a few months of being in a long distance relationship we went on holiday where she asked if I was still in touch with any of my past partners. I denied I was but in truth I was but I wasn't engaging in any sexual content. I stopped the contact with them and saw myself wanting to have a long term relationship with my current partner.

My previous partner that stayed with me still had personal items in my house and I wanted to return these as I felt that was the best thing to do. So I contacted her to get the address to send the items to, this then started a conversation where she was reminiscing on our past but I didn't respond back. I sent the items to her and thought that was that, but what happened was my previous partner started sending messages to my current partner.
She wrote stuff that was not true (saying we were getting married etc) and even described our sex life !
This obviously caused a big issue as it then came out that I was still in contact with her after I said I wasn't, even though I wasn't trying to rekindle anything.

This then started weeks of my current partner of going through my emails, facebook account, pictures anything about my past so she could find more information.
The issue got bigger and bigger and if there was anything that reminder her of my past all what was found was taken up again and again.

What I want to know is how can I sort this mess before I lose the woman I love