Ok, here is the run down and details, I need help

So basically this is where I am at. I have not called her much lately, and I am very emotionally detached from her now - but I still want to figure out what's going on.

I suspect her ex-boyfriend to be visiting her when I am not there - and this is what leads me to suspect it.

- In September, for 10 days, her phone use was odd - She would pick up during the morning and early afternoon, but after a certain time, usually 3 - she would stop using the phone entirely. Remember, I gave her this phone - so I suspect she had to hide it from her ex-boyfriend if she was still involved with him. If I called her at 6, I could expect a call back as soon as she woke up the next day, like clockwork.

- Aside from the phone use, I tried to go over her house 5 times during those 10 days- and each time she gave me an excuse. (i.e I'm sick today, I forgot my phone somewhere, etc)

- Before that, I could go over any time I'd want, she'd always answer my phone or call me back in minutes, so I noticed the change immediately.

-And then - at the end of those 10 days, I was able to get some information from a friend that her and the ex-boyfriend had fought and broken up. The day after they broke up, her phone use went back to normal - i.e I could call at night and she'd answer, I could come over at any time, etc.

That was the most proof I had. Now, when I started to date her - I found out she was still with the ex-boyfriend and broke up with him after she knew I was secure with her.

OK, I'll let that slide since she was probably confused. But this month, the same chain of events happened again.

- For almost the same length of days this month, 10, that happened again..but then it stopped, just like last time.

What the. Maybe she goes back with the guy for 10 days a month and then quits? I am really confused.

I don't yet have any evidence, aside from phone suspicions, which could be something else entirely too.

Now, here is my plan:

I don't have concrete evidence, but I know she's done some wrong stuff in the past.

So I call her, tell her I won't accept lies - and that I found out everything. Then I hang up, and don't answer her for 2 days. This will be the true test of her intentions - we will see how she reacts.

Any ideas on that?