Jealousy without reasons :(

Hello girls! So here's my problem, I get really jealous when it comes to my boyfriend. Im 17 and he's 18 We've been together for 8 months now and he NEVER has given me any reasons to not trust him, except that I absolutely hate that he likes girls on fb, instagram etc, it makes me feel so insecure! he stopped doing it (i think so) because I told him it makes me really mad and sad but just the thought of him thinking about another woman makes me sick. He's really handsome and everytime I know about a girl who likes him and he's friends with her on fb (even tho they dont talk) I ask him to delete her, I feel more secure like he only wants me. I dont know if it really is a problem, I mean I dont try to control him in anyway tbh I let him go out with his friends lol i mean i dont get angry at that I give him his space and he gives me mine. I used to feel so comfortable with him but since a few days ago I just think about all the girls that like him or the girls he sees everyday on school, social media and I get mad at him without a reason :( it makes me feel bad cause im only getting angry at my own thoughts not real reasons, what can I do to solve this? I think its bc i have a low selfsteem, please tell me your opinions