What do I do about my boyfriend's obsession with his mother?

My boyfriend is an only child to a single mother. He is constantly texting and calling her when he's with me, which is every other night. I can't even have him to myself for just 24 hours. It's been 7 months and only getting worse the closer and closer we get. What do I do? How do I approach this subject? Suggestions pleaseee! it's just making me crazier and crazier.
What do I do about my boyfriend's obsession with his mother?
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