UPDATE (28M/26F): She came back, we got the label back, then I found out she'd been seeing another guy

Quick recap: She dumped me late June citing religious differences. I blocked her, stopped initiating, and applied the formula. She called almost daily, initiated every meetup, and things escalated fast.

What happened since:

She proposed exclusivity twice, said she wanted to rebuild stronger, and invited me to her graduation where I met her mother. I held my standard the whole way — declined the errands and small favors, told her I don't do friends with benefits with a woman I love. Eventually she agreed to the label and we were officially back together. She started talking about marriage and kids.

Then it fell apart. I went through her phone — more than once, I'm not proud of it — and found she'd been in contact with a guy she'd told me was just a friend, including messaging him the day I found out. I confronted her. She admitted she'd dated and kissed him during our breakup period in March/April. They'd also exchanged birthday gifts, including one in April when we were still talking before the split. He's her coworker. She texted him that they were done and blocked him, but she refused to let me read their conversation.

For the record, I was dating other women during the breakup too.

I told her I'm ending it. She spent the night begging me to stay and has been promising to change and fight for us. Last night she showed up at a bar looking for me with no money and waited an hour for me to pick her up.

We had a solid 3 year relationship before all of it with a lot of love and care from both sides, with plans to get married this August.

Where I'm at: I told her I need a week with no contact before I decide anything. Two things are bothering me the most. She kept contact with him throughout the entire time. She had lied to my face when asked point blank multiple times.

Questions for the sub:

1. The kiss apparrently happened while we were broken up and I was also dating — but the concealed contact continued after we were back together. How do you weigh those differently?

2. Is there any version of this that's rebuildable when the guy is her coworker?

3. For anyone who's been here — how did you stop checking? That's the part I can't seem to fix, and I know it's mine to own.