Im having problems with my bf :´( Can someone help please?

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Hello im a guy im 15 years old. About 6 months ago i met this guy on instagram. We started texting more. We became best friends and had an attraction. I was straight at the time. He told me he had feelings for me. He was openly bi. We still were bestfriends. I hid my feelings because i thought it was just teenage hormones. After all that i told him i liked him and had feelings for him too. Then a few weeks later we started dating. We met eachother for the first time after that. Now its about a month later. The problem is we argue sometimes. He has trust issues and he likes to just leave whenever we text. He would make me feel alone. Well yesturday some stupid people text him saying i was flirting. I didnt even know those people. He said he didnt know what to believe. I was sad all day and so was he. This morning he wrote me a letter saying sorry and stuff. I love him so much. Hes the man i want to marry one day. I feel like if we broke up i would never want anyone else. He told me he will never break up with me and i would never break up with him. The main problem is our arguing. Is our arguing because of our long distance? And can i expect us to be together forever? Please help