How to handle relationship with the Girl?

My girl complained to me of a boy who was trying to get closer to her. She told me that she did not approve of this. She owns and runs a shop here. She also told me that he visited her for about 4-5 hours in the afternoon. On Jan 31, I returned to my town after a month and went straight to meet her at the time of closing of the shop. What I saw that she was standing next to him and was jumping with cheer. I was taken aback and decided to hold in my car. Just before closing the shop, she was too close to him and both came down to car park. They again spent 10 minutes before going into two different directions. Before my returning, I had texted her of my return plan etc. I was quite upset, as I have been partially financing her business. I sent her a message to which she did not reply full night. I then lost cool and sent her another message after 24 hours stating that if she did not have time to respond my messages, I am taking this liberty to block her everywhere. Now she replied what wrong she had done. I have not responded to her since. For your information, this boy has ill-reputation due to his involvement in illegal activities. My question is "What should I do now? Shall I forget about her?". She has been telling me a lot of lies for one year, which I found out. I shall appreciate your kind advice.