Communication. Communication. Communication. Don’t try to strategize. Don’t try to manipulate the situation to your desired end. And most of all, do NOT “should” him. He is under no obligation to meet your needs or figure them out for himself, and same goes for you. It’s just a question of if he is naturally inclined to meet your needs and act according to your values after you clearly communicate them to him. If he is not inclined, then it’s up to you to decide how far you’re willing to level with him or if you would be better off pursuing a relationship with someone else.
Learn to distinguish your subjective STORIES from what you are actually feeling. For example “I feel like you don’t love me” is NOT a feeling. Putting “I feel” in front of some statement does not magically make it valid. “I’m scared this relationship might not last”, also not a feeling. Any sentence starting with a “You…” is a story. More truthful: “when you don’t message me in X amount of time, I feel insecure, and I start to worry about the future of the relationship”. Now you’re just speaking candidly, honestly, saying what is actually happening. You’re not putting blame on him, just acknowledging something that hopefully everyone can agree is happening (he’s not messaging you), and saying what the impact is on you emotionally, and what kind of thoughts it triggers in you. He’s following some girls on social media? Can everyone agree that’s happening? Okay, how does that make you feel AND, distinct from those feelings, what does it make you think? Please also flip it to positive “when you give me flowers, I feel love and I think this relationship is going well.” Clear, straight-forward communication without shoulding. You can also do it on something that hasn’t even happened “I’d love to go on a vacation together some day, if we work together for that goal, I believe I’d feel secure, and I’d believe you love me” (you’re young and still learning your likes and dislikes, so please be aware that sometimes some ideas don’t turn out as great as you hoped, and that’s okay). Feel free to try to find a way to make the conversation more natural but stick to the same logic.
You may want to look into this: https://pastebin.com/ZHhS044M
And especially this: https://en.wikipedia.org/wiki/Nonviolent_Communication
Well this is where you can ask yourself some questions. The shoulding applies to you too. You “should” not be any different from what you are but being very insecure might not be helpful in having your needs met. You can try to take steps to reduce that insecurity. Or you can continue being insecure and pursue a relationship with someone who is willing to go the extra mile to not trigger it. That may not be easy, but you also might get lucky. Are you okay with that, or does that also make you feel insecure?
Put aside the convoluted projections, strategies and what-ifs. You’re just trying to have your needs met, and he is trying to have his needs met. It’s up to you to figure out if you can do so in unison or not. But the thing is, you WILL find out eventually. You can anxiously wait for the conclusion, you can play around and have fun while you figure out the conclusion, or you can get to the conclusion as soon as possible. But the conclusion is inevitable regardless of how much time you take to get there. Trying to force him to be any different won’t change that. You pretending to be any different from what you are won’t change that. But I can say that in general, the more people stray away from what is true, the more they tend to suffer.