She had seen him a couple of times, gazing at other girls he found interest in but because he was afraid of hurting her, he wouldn't pursue his heart's desire.
She knew he tried to make it work, he fought against himself so many times but what can the body do when the heart has other plans?
So he stayed in the relationship without loving her and also not betraying or humiliating her by cheating on her.
Beverly thought she was selfish when she didn't let him go even though she saw he was hurting, she felt she was the only one receiving in this relationship and never giving, only enduring and trying to make him happy.
Although she understood that she was only beating a dead snake, she has no intention of letting go. She just can't live without Fin, not after all they'd been through.