What’s going on

Why would a guy you’ve been dating for almost a year suddenly stops having any interest in having sex with you and finds any excuse to get out of it after promising they would. I’m just lost for why this is happening and I’m really hurt. I know I’m new to the topic of sex and I don’t preform like a porn star and I’m not really experienced but I’m giving it my best and it seems like he’s not interested in being with me anymore I’m just hurt that he’s not telling me what’s going on he gets my hopes up and then backs out. What’s wrong with me??