I'm in love with someone I can't have and I can't get over him what should I do?

So it all started back In 2018 when I fount a boygroup. I started listening to them because I liked their music but I started liking one of them. At first I was like okay it's just a crush but as time was passing by I fell so hard Inlove with him. When I see him with girls I start crying and feeling sick to my stomach from crying. I don't want to be a toxic fan but I can't control it. Every time I was like yeah I got over him then something was going wrong and back again even deeper. I don't know I feel like he's all that I have I can't move on he is really important to me. I feel like I don't deserve to be his fan