This girl is causing problems in my relationship

My boyfriend was talking to this girl before we met. We got together and he let her know to be respectful and cut it off. She recently came back from school and he went and saw her late at night. It really made me mad because he didn't even tell me about. He tells me she says she's over the whole thing, but I have a feeling she's not. She went out of her way to help him get in school and he says she helps her which I am so thankful for. I texted her and thanked her for supporting him, and let her know she's a good person. She did say I appreciate that, but not once did she say thank you. I also told her since she had his back she can text me anytime and I will try to be the same with her. She had the nerve to respond to my message saying "Lol. Goodnight." I felt like that was so rude because I went out of my way to be nice to her and let her know I have no problems with her. NOW I don't like her. My boyfriend told me earlier this week he told her that they couldn't talk anymore. Her bestfriend called him yesterday and asked when is she gonna see him. I also feel like this other girl is trying to cause drama in our relationship. I feel like the girl he was talking to still likes him, and I feel like the other girl may be lowkey trying to get at him herself. She has a boyfriend but she added him on snapchat because she says she " wanted to see what he does." Did I mention it was after we started dating. What is the best way to handle this situation? I know my boyfriend isn't a cheater, but right now he is allowing other people to mess with his head. It is creating more drama for us and I don't like it. Help?

Yeah i agree as much as you want to blame the girls (which are clearly not helping the situation and doing it knowingly) it comes down to your boyfriend giving you reason to doubt him. Tell him how it makes you feel and if he cant understand your point of view and be accomodating to your feelings you can find someone who will. Go with your gut instinct but never allow yourself to be treated anything less than you deserve x