How would you react if she was spending time with another guy who likely has romantic interest in her?

Ladies, just want your perspective. I want something exclusive and it seems to me like she wants to at least keep options open.

Context: I’ve been dating my neighbor for almost a year. She’s going through a divorce, and she’s been emotionally up and down during the time, and now she seems like she’s on the mend. We spend a lot of fun time together. I told her I see future with her, she says that she sees the potential for a future with me, wants to move very slowly (coming out of a divorce, having hard time fully trusting/committing).

She’s always told me that she’s not seeing anybody else. Recently, I’ve seen some texts pop up from a guy. She has never mentioned him. I typically would not care, but in this case I saw the text which read, “if you’re up for it, I’d love for you to come out tonight”.

This made me uncomfortable, so for the first time, I asked her who he was. She was a bit avoidant/not exactly clear, but he’s someone that she met through her friends. I assume it’s her friends trying to set her up as she’s recovering from her divorce. She says it’s not romantic. He also got her a U. S. Open tennis ball with her initials on it (she’s a big tennis fan), and she had been out to dinner with him alone.

The text, the personal gift, the dinner, all came as a surprise to me tonight and I couldn’t help but feel that at least she’s keeping her options open. I also felt disrespected. I understand she’s going through a VERY TOUGH life event and doesn’t want to jump into something serious right away, but I also let her know after seeing each other for almost a year, I developed strong feelings for her, and I could not see her with someone else.

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3 d
Update: As a reminder, she lives right above me. I heard the bed creaking above me. It was her and that guy. I was devastated not only for the betrayal, but also for the humiliation she caused me and how little consideration that she had for me. and it turned out that she was with him for most of the year I was dating her. I'm seeking therapy to get over this, and it makes it even harder that she lives right above me. So every sound I hear makes me relive this moment. If you have any tips LMK.
How would you react if she was spending time with another guy who likely has romantic interest in her?
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