Make me feel better 😢

I'm extremely anxious because my boyfriend is going to work and travel. He's leaving for almost four months (the whole summer here) and I really get too sad everytime I think about it. He'll travel in december and each day I'm more anxious but I also want him to be back already and I want everything to be okay as now. I'm really scared that trip could ruin our relationship, he always says it won't and I do trust him but I don't want him to be away for so long, we've never been apart for such a long time and I'm really scared😔 I don't know what to do to feel better about it, I overthink too much. Please cheer me up 😪