In the early days of The Big Bang Theory, it was hard to imagine Sheldon Cooper in a romantic relationship - and he was the only one of his friends who showed absolutely no interest in dating. However, when Raj and Howard created a profile for him on a dating site, they found him the surprisingly perfect match: Amy Farrah Fowler.
At first, the two had a not-actually-dating relationship, despite all evidence that they were a couple, but after some ups and downs, the two end up married (and sharing a Nobel Prize). In so many ways, these two are the ultimate perfect nerd couple, but in other ways, they were absolutely toxic - who would want a relationship agreement?
Toxic: Sheldon's Jealousy
Sheldon has some serious issues when it comes to jealousy of Amy - even before he would admit they were dating. He got angry with Leonard after he attended a wedding with Amy (admittedly, Sheldon did wrongly assuming that something happened between them), he got jealous when she was too busy with work, he is jealous of colleagues, jealous of friends, and he's not particularly good at expressing his jealousy in a healthy way, either. In many ways, Sheldon's possessiveness is one of his most toxic traits.
Perfect: Identical Ways Of Viewing The World
Sheldon's quirkiness is generally treated as a joke on the show, but seeing him with someone who had many of the same quirks and ways of looking at the world was refreshing. It made the point that Sheldon might not be like the majority, but that there is still someone who thinks just the way he does. These two understood each other, had the same sense of humor (and ability to miss jokes or social cues), had the same passions, and that makes them a perfect pair.
Toxic: Sheldon Looks Down On Amy
Admittedly, Sheldon looks down on everyone he meets, as he believes that he is the smartest man in every room (and he is usually right). However, he can often be condescending and dismissive of Amy, and that's not healthy in a romantic partner.
Thankfully, as the show goes on, Amy (and the others) help him realize why his language can be hurtful, and he starts to change things - and to show Amy the appreciation she deserves.
Perfect: Created New Projects Together
From Fun With Flags to a Nobel-Prize-worthy theory, Sheldon and Amy are passionate about the same things, and spend time creating new projects together. Having mutual interests and taking time to build and create together is hugely important, and is one of the things that make these two so good together. This is definitely a relationship built on mutual interests, and the two treat each other as peers (most of the time).
Toxic: Sheldon Treats Amy Like A Mother
Sheldon is surprisingly helpless in the world, for someone who is as brilliant as he is. For a long time, Leonard and Penny were de facto parents for him, but when he gets into a relationship, it means that he can find a new mother-figure in Amy. She is often seen taking care of him to an extreme degree, and he often relies on her, rather than acting as an equal partner in the relationship.
Perfect: Amy Knows Where To Draw The Line
Unlike Leonard, Amy is actually very good at deciding where she will draw the line with Sheldon, and telling him when he behaves in a way that is inappropriate. Perhaps it is because she can be just as blunt and straightforward as Sheldon can (while Leonard is too anxious to speak out this way), but she is one of the few members of the main gang who really calls him on his behavior.
When he doesn't behave well at a wedding, she simply refuses to take him to the next one. When he acts inappropriately, she has even left, when she truly believes that they cannot get on the same page. It's just the kind of honest and calm boundary-drawing that Sheldon needs.
Toxic: No Real Friends Outside 'The Gang'
This is true of everyone on the show - and really, of many sitcom friend groups, as it simply makes storytelling easier. However, there's something pretty toxic about the fact that Amy has basically no friends until she meets the gang, and then she and Sheldon never really make friends outside of it - and when she tries to, Sheldon's jealousy often rears its ugly head.
Perfect: Fit Into Each Others' Friend Groups Perfectly
While some might find a lack of other meaningful relationships to be a problem, others would see this as a plus, because Amy fits so beautifully into Sheldon's existing social circle. In many ways, her relationship with Penny and Bernadette actually brings this whole group closer, rather than having relationships drive them apart.
Toxic: The Relationship Agreement
The biggest issue with the relationship is this one - although it seems that Sheldon and Amy are both happy with it, so perhaps it's not an issue at all! However, in most relationships, the idea of a written legal contract, specifying every detail of the relationship and how it will unfold (down to the frequency of coitus!) would be completely unacceptable. Of course, Sheldon has agreements for everyone, and this is certainly one way of making expectations clear.
Perfect: Brought Out The Best In Each Other
Over the course of the series, Sheldon and Amy's relationship brought out the best in each of them. When they first met, they struggled to fit in socially (even with their own friends), they didn't expect to find love - but through their relationship, they both grew. Sheldon became much more caring, and much more concerned with how his behavior affected others, as well as more open and vulnerable. Amy, meanwhile, also opened up - she became more confident, she started dressing exactly how she wanted and being far more proud of herself, and it was incredible to watch.