Ok, starting with Black Cat…
Black Cat and Spider-Man happily swung around together for a few months until he decided to reveal his secret identity of Peter Parker to her. He pulled off his mask and told her his real name. She was stunned and asked him to put his mask back on. Yeah, it turned out she was in love with Spidey, but the thought that under the mask he was just a normal guy revolted her. This drove a wedge between the couple, yet they continued patroling together, though SM didn’t flirt as much.
SM began to discourage Cat’s crime fighting with him since she had no powers and could more easily get hurt. Cat refused and sought out a mystery benefactor, later revealed to be Kingpin, who unlocked her latent mutant bad luck powers, which duplicated the gimmick she’d used when she first came on the scene (setting up booby traps ahead of time so it appeared bad luck was befalling her opponents.) Cat never told SM about this and continued to fight crime with him.
Over time SM found he was having worse and worse luck and went to see Dr. Strange for an explanation, at the same time Cat went to see Kingpin for the same. Kingpin explained to Cat that her powers would not only affect those who meant her harm, but those she was close too as well, until “where there is a point where one’s luck can get no worse.” Meanwhile, Dr. Strange discovered a bad luck aura affecting SM and removed it at the source. Bad news for Black Cat who was fighting Kingpin’s goons at the time and got her butt handed to her. This led to the revelation to SM that it was Cat who was the cause of his recent misfortunes. They argued and went their separate ways.
SM didn’t date much after that point, until Mary Jane came back from wherever it was she ran off to a few years prior. MJ, still the party girl, and Peter struck up their platonic relationship again. One day, Peter tried to kick MJ out of his apartment because he didn’t need her party attitude when he was depressed. She refused and began to look at Pete in a different light.
Months later, Puma burst into Pete’s apartment and the two fought as MJ knocked on the apartment door. She heard the fight and eventually broke the door open as Puma took off. Pete tried to cover up with another excuse but MJ confessed she knew he was actually Spider-Man, and had since she’d seen him crawling out of his window when they were teens. She’d kept up the party girl facade around him for fear of getting too attached to him. This led the two of them to become closer friends than ever as she then explained the details of her troubled youth with her alcoholic father.
They went on this way for months until one day Pete reevaluated his life and decided something was missing. He asked MJ to marry him. She said no, and instead, ran off to Philadelphia to confront her family. Pete followed her and after beating down a pursuing Spider Slayer, Pete convinced MJ to marry him. Shortly thereafter (1987) they were married (in the comic book [ASM Annual 21], comic strip, and Shea Stadium.)
They were happy at first, despite the fact that about two issues later Venom terrorized MJ by breaking into their apartment wearing the black costume SM was currently sporting a duplicate of. That was just the first of many times Pete’s alter ego would cause marital stress. Though not many of SM’s enemies knew his secret identity, the fact that SM put his responsibility to the public above Pete’s respnsibility to his marriage resulted in a strain between the lovers.
The straw that broke the camel’s back was the return of the Green Goblin. (IRL, it was the return of John Byrne, but we’ll stick with storylines.) MJ was pregnant with their first baby. It appeared to the reader that Goblin was behind the scenes, plotting to kidnap the baby at birth by inducing labor and having a nurse on his payroll steal the baby while the doctor informed MJ that her baby was stillborn. That Pete was out fighting Goblin while all this happened to MJ was more than she could take. MJ moved to LA to get away from SM.
Over the year or so (comic time) that she was gone, MJ worked on her acting/modeling career and on the outside appeared to be doing well. She and Pete kept in touch from time to time but never reconciled. They agreed to meet in New York to try to work things out but SM was trapped in an astral form after an adventure with Dr. Strange and couldn’t meet up with MJ, despite the fact that he wa actually there in spirit. Pete and Aunt May (who was dead, but got better, and also learned Pete was SM) flew to LA to see MJ. Things went pretty well but they still stayed apart.
Recently, MJ and Pete spontaneously decided to fly to each other’s respective cities without the other knowing. They missed each other of course, but in a wacky set of circumstances, found each other when both of their planes were laid over in Denver. The two of them talked (in between SM guarding Doctor Doom against assassination attempts with Captain America) and decided they would give their marriage one more go.
Some of the above may be slightly out of chronological order, but it should be mostly right. If anything is confusing (ha!) lemme know.