18F! My bf(18M) disappears for hours & lies about it!.

I really need some genuine, outside perspective because this situation is completely killing me from the inside. I’ve been in a relationship with my boyfriend for 2 years. The first year was absolutely amazing, but for the past 6 months, he has been acting incredibly erratic. He constantly goes completely MIA for 2 to 3 hours at a time with zero communication. I have asked him thousands of times to just drop a text or send a snap so I don't worry. He will do it for a day or two, but by the third day, he reverts right back to disappearing.Things got so exhausting that I actually tried breaking up with him a few days ago. He begged me relentlessly to stay, so I gave him another chance. Since then, he is trying to fix things in other ways—he’s been giving me gifts, trying to talk to me more, and putting in effort elsewhere. However, the core issue hasn't changed. He is still disappearing, just slightly less, and I've caught him lying. For instance, he will be out with his friends but will make up an excuse that he was busy doing a course or studying.I feel stuck in a loop. He says he loves me, and his affection and gifts make it hard to leave, but the lack of transparency and the lying is breaking my trust completely. How do I handle a partner who does everything to keep me from leaving, but refuses to fix the one major thing that is breaking the relationship?