I couldn’t finish from sex tonight and I feel bad about it

I am F(20) and my bf is M(19). I have sex with him probably 2-3 times a week and it’s usually great and I always finish. This past night we had sex I just couldn’t finish. Sure, sex felt nice, but it wasn’t as mind blowing as it usually was and I just never got to the point where I felt I was going to orgasm. Is there something wrong with me? I feel really bad that I couldn’t finish because it makes him feel bad. Has this ever happened to anyone else? I just don’t want it to become a new thing that happens every time. All input is helpful!