Titty fuck

So my boyfriend loves the idea, he has done it with multiple women in the past and seeing that I'm relatively small bust wise - I feel so embarrassed and ashamed. His ex was a DD and here I am barely a B. He loves me and never makes me uncomfortable about my breast but I do notice him being more attracted to woman with bigger breasts..any smaller woman titty fucking ? Thoughts, opinions , ideas? Please help ...We've been together for years and this has been brought up a few times