Finn is just happy to have her back. He thinks they are an end game couple, and they may very well be. It feels good to see them together again, and I don't think either of them have their feelings hurt by the other. They aren't at the right places in the lives to be a couple right now, but eventually they could make it work again.
Someone has to be there to pick Rachel up when she gets hurt by Brody. It's not explicit, but it appears that "I Do" exposes Brody as a male prostitute. This Hung-esque plot could explain how he gets money to live on, but will not be a very nice surprise for Ms. Berry, especially when Brody is preaching honesty earlier in the night. Granted, she isn't entirely honest with him, either, but it's not quite the same. They appear to be moving towards a big relationship blow out.
Next up, Artie's (Kevin McHale) romance with Betty Pillsbury (Ali Stroker), Emma's niece. Do they have to try to shove the two people in the chairs together? Emma's attempted hookup of them feels false and vaguely insulting. Plus, I never cared for Stroker during her run on The Glee Project, and even though she did win second place last year, I didn't expect to see her pop up now, especially without being featured in a musical number.
Why does Betty show up at McKinley? She's not a student there. She shouldn't be able to just come and wander the halls, during a school day. Ugh.
Lastly, we get to Marley (Melissa Benoist) and Jake (Jacob Artist). Jake wants to give her a special Valentine's Day, and lacking being a romantic himself, he lets Ryder (Blake Jenner) take the reigns, including a cheesy in-class serenade of "You're All I Need to Get By," which would not be allowed in a real school. Marley sees right through it, but only tells that to Ryder, not Jake, reigniting the love triangle.