Avoid attempts to become number one.
It is impossible. It is always going to be mama first for your boyfriend. Your attempt to make him consider you the top priority in his life is just one sure way to distance him from you. Let him have his freedom to always choose his mama first. This attitude may even endear you more to him.
Befriend his mother.
Mothers of mama’s boys are naturally antagonistic to their boy’s girlfriends. But, try to look at it from the viewpoint of a concerned mother who wants her son happy and is at the same time terrified that a girlfriend would separate him from her. If your boyfriend’s mama is one such concerned and terrified mother, assure her that you are not trying to break their mother-son bond and want to maintain a good relationship.
Make your relationship with his mother a priority.
Meet her whenever possible and wish her well on birthdays and special occasions. Make her your ally and not an adversary. Give the mother and son more opportunities to be together by inviting them to your family get-togethers, special occasions and celebrations at your home.
Pay no heed to irritating mama-related remarks such as "You definitely cannot cook like my mother," or "You need to learn organization from my mother," that will inevitably spew out during conversations.
Talk to your boyfriend regarding your feelings without sounding demanding.
Tell him that while you do not want to break their mother-son relationship, you would like a little more attention from him. Sometimes, miracles do happen, and he might just understand you.
Do not attempt to change your personality to suit your boyfriend’s demands.
You are your own self. Recognize what is coming from his relationship with his mother and what are reasonable demands for your relationship.