Hope for the minimum encounter and be prepared for the lengthy secondary. Bear in mind that CBP's concern is that you will overstay and become a burden on the US (no different for the USN entering Canada, UK, Australia or any of a host of other countries).

The only reason the boyfriend issue matters is that you might be tempted to overstay.

Thus, have clearcut documentary proof of your intent to return when scheduled, funds to support your stay and contact information for the boyfriend and relatives.

Whatever you do, do not lie. Lying includes withholding details which a reasonable person knows are significant and it also includes playing word games. Lying becomes the basis to pop you on the next flight back, so don't do it.

There is nothing to be nervous about and there is no reason to seat this. Just have the stuff ready if you are asked, but don't start pulling it out until challenged on it.

Remember, although there is all kinds of snark above, this is not a policy debate. Maybe it ought to be easier to move between countries, but it isn't.