Please do not get this done just because he wants it done. He shouldnt date girls with small tits in the first place. BTW small tits are fine just so you know. Plenty of men have no problem with them at all. Maybe he watched a lot of porn. Who knows but it doesnt matter because he knew in the beginning. And if it bothered him that much he should have moved on but he didnt. Thats not your fault! I dated a woman in my mid 20s who got implants and its no walk in the park. I talked to her like 10 years later and heard she had complications with them. I also had an aunt get them and one of them popped by that was back when they first came out. Maybe nowadays they are safer idk. But its still a huge surgery. Heres an idea:

Tell him you dont like the size of his dick anymore and youll get bigger tits if he gets a bigger dick. See how he likes it. Should shut him right up.