What can I do to improve myself?

Hi guys,
so i’ve been dealing with insecurity for a long time and I don't know how to snap out of it. i freak out that my boyfriend is cheating on me whenever he doesn’t answer my phone calls. i feel like he has someone at his house or he’s talking to someone else or he is interested in someone else. i think i feel this way because in the past he has DMed a girl saying she was pretty, beautiful or gorgeous and it made me really sad. when i asked him why he did that he said that we barely knew each other. he also followed a bunch of girls and liked their bikini pictures. so i feel like he will do it again when i least expect it. so as of a year ago he has been sleeping super late and waking up late (around 2 or 3pm) so when i call him during my lunch break he won’t answer me. so i always wonder why and i start freaking out and thinking that he is cheating or talking to another girl that he is interested in. let me say that he has showed me his DMs and his likes on instagram and he is not doing anything wrong. i just however have a really hard time accepting it. so whenever i do get him on the phone i automatically say things like “you’re talking to someone aren’t you?” or “you’re interested in someone else aren’t you?” and he says “no” and the past few times he’ll say “geez your so insecure” or say “do you have anything else better to do than bother me?” or “are you finished? i have better things to do then be on the phone” it really hurts my feelings and i understand that my insecurities bother him, but he shouldn’t be so rude to me either. he’s never been rude to me before but he has been very rude recently. I don't know what to do about my insecurities and how to snap out of it.
What can I do to improve myself?
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