sex!!!!!

So me and my boyfriend everytime we try to have sex we are all into it and it starts off good and very intense and we are so into it we start  taking our clothes off we're both so excited and when he's ready to go in his D doesnt go down but its not all the way up and hard like it supposed to be and we have tried like that but it doesn't want to go in either, we tried it 3 times and all 3 times the same thing happens, im scared that im not that attractive to him in that kind of way. He tells me its weird, that way after me this never happened to him like with girls he never loved or liked and now that hes with someone he really loves this all of a sudden happens! 😪 does someine know why ir how i can be with him like without anything like this happening