<human>: Can you succinctly summarize the text in 1-3 sentences?

gf goes on trip with family member but I suspect that she is there with ex lover of few years. A extraordinary month love blossoms but lies about the trip persist. During the trip and after much denial of said relative she admits to be there with the ex. The trip has been planned for a long time and would cost a fortune to cancel . After she admitted who she was actually there with I ask if anything sexual has happened and she says no. 
If she has been lying to me about the entire thing how could I believe that she is being truthful about sexual encounters? I really do love this girl and I'm getting mixed feedback from family and friends.
<bot>: what should I do, trust that she was on a trip with an ex and had no sexual encounters after lying about the whole ordeal and give her a second chance? Or drop her from my life completely. Help Me!