Is that love or more guilt he feels? He has a hero complex and part of that is not hurting people. I think the idea of dropping Tamara just because he saw Emma again goes against whatever moral code Neal has. And Emma wasn’t back in his life, not romantically. She was trying (not well) to make it clear that she had moved on. Her walls went up and he didn’t want to hurt anyone because he is a good guy.
Guilt was certainly a part of it. As was his lifelong desire to have someone he felt safe with and could call family. Here’s this girl who loves him, who is even completely understanding and accepting of the messed up reality that is his life story. When’s he gonna find that again? Meanwhile, he’d really rather patch things up with Emma, but she’s got all her walls up, insisting she’s not interested, so as far as he’s being forced to accept, Tamara’s his only option for a shot at love and happiness. And she’d been so very understanding, and had done nothing to warrant being automatically dumped and hurt, so how could he live with himself if he did that to her?