First off, I'm a man and I prefer small boobs (not that it's something that's ever affected my decision to date someone). I'm sure I'm not alone, in fact I suspect for many men the thought of big boobs is far more appealing in theory than the actual reality of them.
Anyway, my now partner was in a similar position to you when I first met her, she said it was a self confidence thing, although I think she meant small boobs affected her appearance clothed rather than purely in the bedroom. To me, she had an amazing figure - size 8-10 with in proportion b cup boobs. But she wasn't happy with them.
We weren't in a serious relationship at that point, although I still tried to talk her out of having them enlarged. I was concerned that she still wouldn't be happy, that they'd look 'fake', and that she couldn't really afford it either. I'm not sure if the self confidence thing was actually trying to reattract her ex. She went through with having surgery and went from a B cup to a C.
I have to say they do look great (not better than before, to my eye, but just equally as good). They're still very natural looking, and not out of proportion to the rest of her figure. I've not noticed any real change in her personality or self confidence though, either that's a very sub conscious, deep rooted thing, or it hasn't turned out to have had a positive effect. I did suspect her slight unhappiness was due to other reasons (the ex). I'm not sure if she's actually a bit underwhelmed by the lack of improvement to her self confidence, but she does say she's happy with them now. She's also well over her ex now and in many ways in a much happier place anyway.
That's not the end of the matter however. About 6 months after having the implants, she started to get ill. After a year she was chronically ill. Her GP was useless, and eventually it got so bad I pushed her to go to A&E. She was diagnosed with an autoimmune disease, and was hours/days away from death. She spent a month in hospital and had life changing surgery.
Now that could have been a total coincidence (and most women who have implants don't get any side effects like that), but have a google for breast implant illness/implants and autoimmune diseases.