Jealousy

Hello! I have a friend for about 5 months. I'm 16 and he's 24. Maybe it's enough for someone, but that's not the problem. I study in another city and in fact we only see each other on the weekends. He is quite sociable and I am quite jealous. Quite often, without giving reasons for jealousy, I was quite naughty. I am very worried about my jealousy and maybe this will separate us. He's had a lot of girls and that fact really worries me. I'm afraid he might get too bored and find another one. What to do in this situation, because I feel that it spoils our relationship a lot.