Girlfriend flirting with someone else

I will try to be brief.

I am 46, my gf is a 37 single mom (2 kids)…few months ago she went to a club with some girls, i found out that she ended up flirting and dancing with some young guy of 21. Before i find out she told me that some guy came to her, talked to her while she was dancing, but she refused him and sent him away. I found out that she danced with him, i confronted her with this, and said “yeah, i forgot, we danced a little bit, few seconds, but that’s it”, and she swore that it was it. After a while i saw some videos made at that club, and i saw that she danced in an intimate way with him, several times, and spoke and laughed several times (flirting), and at some point she danced with him on the table, also in an intimate way (when i say intimate, i didn’t see any kissing, but intimate positions, grinding…etc).

I confronted her again with this and she said that simply she forgot about that dancing on the table, because she drank too much that night, and the reason that she danced with him because we had a big fight that day and she just wanted to forget.
The idea is, whatever happens we can talk about it, even if we end up cheating, we can discuss it, so i don’t understand why she still insists on lying.

I am not sure if what i wrote makes any sense to you. But i appreciate your advice.
Thanks in advance.