My boyfriend is homophobic towards his son..advice?

We’ve been together for 3 years, and live together with his 11y/o son. We’ll call his son Jack. Jack does absolutely nothing to make me suspect that he might be gay. But he likes bright colors, which is entirely fine with me (and Jack’s mother), but my boyfriend is bothered when he takes a liking to pink or ‘girly’ colored things.

Some examples-

Jack plays football every year, and last fall they did a breast cancer awareness game. They received hot pink socks and hot pink long sleeved shirts for under their jerseys. Jack likes the shirt, and liked to wear it around the house after the season ended. It visibly made my boyfriend uncomfortable, and he made Jack hang it up in the closet and tells him not to wear it.

Jack spends every other weekend with his mom. Last summer when he was over there, his flip flop broke. His mom let him pick new ones at Walmart, and he picked ones that were black with hot pink straps, and brought them back home. My boyfriend immediately bought him new ones that were blue, and threw out the pink ones.

Recently, Jack has been playing the new animal crossings game. He got a present in the game, it was a pink hat. Jack put it on his character to see what it looked like, and my boyfriend saw and immediately made him take it off.

My boyfriend is only like this with his son. While I realize he’s probably masking it or something, he acts completely normal when interacting with gay men. Yet he acts like his son wearing something pink is going to magically turn him gay, and clearly he’s afraid of that. It makes me very uncomfortable. I’ve brought it up in the past with him, he hasn’t changed. I don’t know what to do. I don’t want to scrap the whole relationship just because of that. I’m very involved with his son, I can’t just up and leave. How should I talk to my boyfriend about this?