Sexual fixations on a mother are common. When young men start to experience sexual desires, a sexy mommy or step-mom are often the subject of fixations. This stems from the fact that they generally manage to get peeps of these hot milfs naked or partially. The full breasts are surely stimulating.
The reality is, that mommy is often a nurturing woman and men are comfortable having thoughts of mommy. As a therapist I am rather happy to assist in facilitating these fantasies. My love of incest knows no boundaries.
Now, I would be interested in what ways your mother or step-mom has induced deep sexual desires in you. Maybe she bathed you as a boy. Perhaps you were lucky to have a mother showering naked with you.
Finally, my ultimate goal is to assist you in recreating the sensations and making you have the best fantasy call about that mother of yours.