Don’t understand

So I’ve always been quite a sexual person. I enjoy watching porn and watching movies with sex and stuff in. And I always think I wish I had that. But when it comes to having sex and intimacy in real life it’s like I go really shy and get nervous or I don’t want to have sex but I just can’t even answer my own questions as to why I don’t want to? I don’t know if it’s because I don’t feel sexy or what? I should also mention I’m 26 years old, been with my partner 7 years and we have 2 kids.