Here's my take on it, trying to take into account Fleiss's bizarre editing style.
1) Andy picked out Bevin from the beginning, much like Aaron picked out Helene.
2) Unlike Aaron, there was a little Bob in him, so he allowed the producers to talk him into enthusaistically participating in other dates.
3) The Pretty Woman date would blow away any man and woman who at least liked each other. It put Tessa in a very romanticized light in Andy's eyes.
4) Meanwhile, Andy and Bevin had a relationship. They fell for each other, they probably went horizontal. Just the way Andy kept touching her, and the way Bevin responded, especially in Pennsylvania, really seemed like the early stages of a real relationship.
5) One thing Fleiss really gets right sometimes is he chooses a leading man who's a true momma's boy. Andy listens to his family, especially his mom and his sister.
6) The Pennsylvania dates forced Andy to see Tessa and Bevin through his mother's eyes. While Bevin is certainly a great catch, and seems more settled, there's no question she wasn't for a long time. It's difficult to look at tattoos like that in the context of a doctor's wife in a conservative, close family.
7) This left Andy with a dilemma. Follow his heart, which was racing from the passion of the early stages of a relationship? Or make the safe choice.
8) Andy had to talk himself into it. "I FRICKIN' love you" is a strange declaration. Like he knew Tessa would fit in perfectly with his life, and all he needed to know was that Tessa felt the same way. It was anything but passionate.
9) The final scene with Bevin was uncomfortable and weird, in context. He really was breaking off a semi-monogamous relationship, reluctantly. He was still touching her intimately, even as he was breaking up with her. If this were real life, it may have been the first of many similar scenes.
10) Tessa is the safe choice, but this is a rebound relationship.
11) Getting back together now will be very difficult for both of them. Andy probably doesn't have that intense passion for her, even though he goes through the motions very well. Without producers telling him what to do, it won't be nearly as romantic an experience.
12) Tessa has to watch the finale, now that everyone is telling her not to. It will devastate her. She will try and rationalize this, but the relationship will be forever affected.
13) Why? Remember that this intense, intimate breakup scene with Bevin took place just hours - HOURS - before he proposed to Tessa. She can't forget that. No woman could.
14) To make matters worse, even if she could get over being the rebound relationship, there's the almost-mocking "he's just not that into you" statement from earlier in the finale. That will sting.
15) You can do a lot of things to a woman, but you can't hurt her pride. On national television, to boot.
So, here are my predictions:
1) Nothing we saw will be anywhere near as difficult as it will be for Bevin to walk into her office for the first time since the finale aired. That will take guts of steel.
2) Tessa will never move to Hawai'i.
3) Tessa will stop wearing the ring within a week.
4) Andy and Tessa will remain friends. Andy will want to keep trying, but he won't pursue it very hard.
5) Andy and Tessa will keep a very low profile. At some point, some reporter will remember that they exist and they will announce, quietly, that things didn't work out.
6) There's at least an 80% chance that Andy will call Bevin, but only a very small chance she will return his call.
7) If he winds up married to any of the 25 girls, it will be the Asian doctor, whose name I can't remember.