Haven't you ever been angry at a partner? Have you ever broken up with someone, or been dumped? Interestingly enough, those actions are usually preceded by bouts of anger. Does it make you less of an adult to get angry?

When I was naive and clueless yes, when I when through life I learned how to act like an adult in a mature way. You cannot change someone with anger or grovel. If a person wants to do something he/she will do it regardless of what someone else wants them to do. They may agree orally and spin tall tales but in the end the inner ego will take over and do it anyway. If you look through OP's post he has been having problems and issues 10 months ago. He was not getting all out of this relationship that satisfies his needs as a human being and that started manifesting itself in him looking for other avenues like having a flirtatious conversation with another person. Since we are on INFP subreddit I am not going to delve into the psyche of INFP but assume that we all understand how our minds work. The result of displeasure and feeling of discomfort in the current relationship doesn't always manifest through confrontation, angry outbursts or one night stands but through subtle things like OP described. His idealized values prevented him from cheating on her. He wants to keep giving the person another chance again and again because we tend to believe in some ideal perfect non-existent entity that can exclusively love and idolize just one person and can be perfect in every single way. Two parts that makes us human are relevant here: one, we function through chemical flows in our brain, so him being attracted to someone else is just a natural course of things. two: as humans with age and time we learn how to control our emotions better and better and behave in a civilized manner and respectful towards each other no matter the circumstances. He can choose to love someone and be respectful towards them and uphold their values and not destroy them, but don't delude yourself by thinking that love is jsut an emotion. Love is more than an emotion. It involves trust, respect, dignity, hard work, controlling urges, being open, honest, understanding and a gamut of other things. Let me give an extreme example. He walks in on her having sex with someone else. He doesn't beat the shit out of that person, he just realizes that this is not meant to be, wishes them good luck and walks away. C'est la vie. I am going to reiterate if she feels( and if he knows for sure) that what he did, is an unforgivable sin for her, she should just go, because if he makes her forgive him with his reasons of love, them staying together for 5+ years or whatever eventually she will want out because this conflict will eat her inside. He has asked for her forgiveness and expressed his regret. It's fine whatever way he chose to do it, I am not a fan but it doesn't matter. What I am saying is that now he shouldn't try to strong arm her into making a decision. If she feels she can forgive him and be in a trustworthy relationship in the future she will do it. Now replace he with she everywhere. Genders don't matter. I would give the same advice to any human being.