That just proves that he doesn't love her more. The complete lack of respect involved in that thinking for the person being cheated on shows how little caring he really truly had for her. He didn't love her on the island. He made her into his guilt trophy object. A manifestation of his previous life that he could pine for. The fact that only after he'd been slapped down did he feel bad for his actions at all shows that he never loved her. The fact that he was only concerned for her feelings because she would find out proves that.
No, it doesn't. Plenty of people have cheated on someone that they love. Just because you cheat on someone, does not mean you do not love them. Plenty of people get back together after one of them cheated, if the cheater is genuinely sorry and if their partner believes they will not do it again.
If he didn't love her, he wouldn't care if she found out. He didn't want her to find out because he obviously did not want her to stop loving him. He almost sabotaged his and Slades escape mission by calling Laurel when he was on the island. Of course he loved her.
Oliver's not a good person. He's a serial murderer. The only change is his actions getting violent. But him being forgiven by them doesn't change anything he's done. Laurel's forgiveness doesn't matter. He still did them. Her forgiveness doesn't change that and he does or will ever do on his own will ever change that.
Oliver is definitely a good person. If he wasn't, he wouldn't be loved by the vast majority of fans. He would have a similar reception to Don Draper on Mad Men if he wasn't, who does lots of questionable thing, and while enjoyed by the audience and fans, plenty call him nasty things for what he does.
Also, the likes of Barry, Diggle, Laurel and others who are good people would not associate themselves with Oliver if he wasn't a good person. He is definitely a good person. A very good person in fact. He regularly saves people and risks his life to help others. He killed people because that is what he was conditioned to do n the island and he thought it was the best way to deal with criminals. He then changed and only kills when necessary now.
Laurels forgiveness does matter. If a person he hurt forgives him, that speaks volumes about him. More than most peoples, if not everyones. Quentin forgave him too.
When he did not want her out on the field? He was right to do that. She had little experience. That is a completely normal reaction. Most people would react that way. It is a rational and understandable reaction. He cared about her and did not want her to get hurt or worse. That was not belittling her at all.
Actions are unchangeable by humans. There's no scale. It can't be evened out. Nothing can by done by his actions on his own..
Using this logic, there are a lot of bad people in the world.
If Laurel forgave him, then he made it up to her. It is as simple as that.