The Girl I’m With Has A Guy Best Friend.

Just to hide names, we'll call the girl Ann, and the guy best friend Samuel. I have been talking to Ann for months now and everything has been going great. However, I am a big overthinker. Before she met me, she had a best friend, Samuel. Now Ann and I aren't dating, we acknowledge that, but we act as if we are. She always reassures me that I have nothing to worry about and I trust and believe her. Her and Samuel have had a past, she has liked him at one point, she kissed his hand before, they kissed accidentally before, she climbs all over him and is very clingy with him, she stays at his house a lot and they lay down together, and he recently confessed his feelings to her which she rejected but she is staying friends with him. I talked about this with her and how I was jealous. She says to me that she loves me but also says that me and her are not dating and neither are her and Samuel. She said "I know saying this is bad but I'm not dropping him, I've known him longer and I won't be dropping him. You know I love you." "I don't know what to tell you. Me and him are close and we are just best friends. You only know all of that stuff because I told you 'cause I'm honest, whatever happens between me and him, I tell you." She also says that she has stopped being "flirty" with him because me and her are a thing and we love each other, and that flirting with him would be fucked up if she was already talking to me. A very important thing that I should mention is that me and her are long distance, but there is nothing that we don't tell each other. I'm sure of it. Again, I don't want her to seem like she's a horrible person with the quotes because she is very, very nice. I think that everything is okay on her end but I am just struggling with jealousy because I know the Samuel likes her, and I wish that I could be the one that she did that stuff with. Also some of the stuff they did was a long time ago but some stuff they still do, as far as I know. I don't want to think she's lying, because I believe her. It's just scary knowing the stereotypical disaster that occurs with stuff like this and I feel that I may be blinded and this very well may be something wrong. I want to talk it out with her more but I don't want to be seen as controlling or anything.