My close friend got into a relationship

I’m sure everyone has or is going to go through this at some point but recently my close friend got into a relationship and I’m feeling a bit jealous. I’m very happy for him and know that he deserves all the best but I’ve realized that I’ve gotten jealous and annoyed with the person he is dating. There is nothing wrong with his significant other and I don’t know why I can’t shake this feeling. Maybe I just miss our closeness that we used to have or it could be that I’m scared to lose a close friend to a relationship again. I just feel terrible feeling these emotions and am probably just worried about our friendship in the future