(1) The Gemara does not resolve this issue explicitly. Abaye attempts to prove that Bi'ah only accomplishes Erusin, but the Gemara deflects this. Rava also attempts to prove that it only accomplishes Erusin but the Gemara deflects this too. Then the Gemara itself attempts to prove that it accomplishes Nisu'in but Rav Nachman bar Yitzchak and Ravina also deflect this.

(2) However the Rambam (Hilchos Ishus 10:1) clearly understood that the conclusion of the Gemara is that Bi'ah only accomplishes Erusin. This is apparent from the fact that he writes "Even if he did Kidushin with Bi'ah he is forbidden to have further relations with her until he brings her into his house......... which is termed Nisu'in."

(3) The Magid Mishneh writes that even though the Gemara does not explicitly decide the question, nevertheless it appears that Abaye and Rava understood the simple meaning of the Mishnayos to mean that Bi'ah only accomplishes Erusin. Even though the Gemara rejects these proofs, nevertheless the simple meaning of the Mishnayos still remains in Abaye and Rava's favor and the deflections are considered rather forced.

(4) The Rosh 1:17 also writes that the Halachah follows Abaye and Rava who attempted to prove that it accomplishes only Erusin. The Rosh adds another proof for this conclusion : the fact that Rav Nachman bar Yitzchak and Ravina rejected the Gemara's attempt to prove it accomplishes Nisu'in. This means that Rav Nacman and Ravina both agree with Abaye and Rava, so this constitutes a strong consensus of opinion and these famous Amora'im appear to carry more weight than the anonymous arguments of the Gemara itself.

(5) The Ran (near top of 6a in Rif pages) also writes that the Halachah is that Bi'ah only accomplishes Erusin. The Ran implies that since the Gemara is unsure about this question, we therefore remain with the smaller chidush: that Bi'ah only accomplishes Erusin.

Kesivah v'Chasimah Tovah,

D. Bloom