I agree about the back of the car bit. I think it is referring to something sexual, not because the character is in love, but he just wants people to know he has someone. I think the part about "you are your mother's only son and you're a desparate one" is perhaps saying the character's "lover" is also in the relationship for the wrong reasons; that is, he is so desparate to carry on his family lineage he is willing to share his backseat with just about anyone.
I agree about the back of the car bit. I think it is referring to something sexual, not because the character is in love, but he just wants people to know he has someone. I think the part about "you are your mother's only son and you're a desparate one" is perhaps saying the character's "lover" is also in the relationship for the wrong reasons; that is, he is so desparate to carry on his family lineage he is willing to share his backseat with just about anyone.