Nice, I feel like Ross always gets the poop end of the break up stick. I think it is important to point out that Ross never would have taken 'copy shop girl' home if he hadn't heard Mark at Rachel's place when he called Rachel to try and fight for her.
Also, I can't be the only person that thinks Mark knew exactly what he was doing. We do find out shortly after the break up that Mark was interested in Rachel. Remember when Rachel and Paolo broke up and Chandler and Joey were convinced Ross needed to be the first guy she talked to after? Well, Mark made himself that guy. He acted like he was a friend being there for support. Well, I have supported friends through break ups before, and if the girl is feeling regretful and like she overreacted and the ex calls her, you had better believe you are sitting perfectly still in the background not making a sound, listening intently to find out what happened. And that is when you are a girlfriend who has never posed any romantic threat. The fact that Mark knew Ross was on the phone and spoke up loudly, two times, is pretty blatant to me. He knew how paranoid Ross was about him and he made it clear that he was in Rachel's apartment hours after their break up.
Yeah, Ross was overly jealous and possessive, but the last time he was in a relationship and his SO started to branch out into new interests (something the he excitedly supported), she ended up leaving him for someone else. So, yeah, Ross should have been more supportive of Rachel's career, but Rachel could have been more sensitive to his concerns. Instead of trying to understand why he was so possessive (reasons that she had the background to know) and working to help him see that the circumstances were different and he could trust her, she just breaks up with him in the middle of an argument on their anniversary. And yeah, Ross behaved inappropriately at her place of employment on their anniversary. But if you switch their genders and Rachel is telling him that his job is just a job and she would like to be a priority sometimes, it wouldn't be seen as creepily possessive. It is a valid frustration to have in a relationship. Being married to someone that works ridiculous hours, I can say we have had almost the exact same fight many times, and it usually ends in a similar way, with us taking a break like the one Ross wanted. Ross wanted to calm down and revisit the topic with clearer heads. It is surprisingly effective. When it is no longer their anniversary and Rachel isn't facing a crisis at work, it is very doable to sit down and have Ross say "I will try to be more understanding of your time constraints, but I need to feel like you are making more of an effort to be with me" and they can work out ways to feel connected with less interaction and she can put some of his fears to rest.
I do think Rachel was right to be upset about his behavior towards Mark and not trusting her and being so possessive. But the fact that she always acts like it was all Ross' fault is completely unfair. She made no attempt to make him feel more comfortable with her situation or try to understand why he was so anxious. Then she broke up with him. I don't know what "on a break" means, but Rachel did tell Monica when she asked about it that they broke up, so she clearly thought it could mean the definitive end of the relationship as well. Yeah, it maybe showed a lack of respect for their relationship that Ross slept with someone that night. I completely understand why it would upset her and make it hard for her to be with him again right away. I don't agree with her basically insisting on him taking total responsibility and labeling him a cheater before she would ever take him back. I feel like she never even acknowledged the fact that Mark was in her apartment the night they broke up, which she knew would upset Ross.
Also, a long term SO who has never once broken your trust or hurt you doesn't exist. I am not saying you should stay in relationships where someone hurts and betrays you, but people are imperfect and life is weird. It is easy to say Joshua could have been Rachel's soul mate because they had a nonexistent relationship where no trust was ever built to be lost. A relationship where Rachel was over pursuing him to feel less jealous of an ex. I am with Monica in that I don't really believe in soul mates. But if there were such a thing, it definitely wouldn't be Joshua for Rachel.
I do believe in lobsters, and Ross is definitely Rachel's lobster.