I needed this thread and didn't even know it! Don't get me wrong, I love me a good romance, but not at the expense of great platonic/nonromantic relationships! So happy to see this thread full of familial bonds and close friendships (and now you've all added so many more comics to my reading list--thanks!).
So I'm pretty big on sibling dynamics, as someone with three siblings herself, and as someone who is both a younger sister and an older sister, so it's no surprise one of my favourite dynamics in my comic is between these two brothers, Seth and Jon:

Half-brothers on their father's side, but for as long as they've been able to say the words, they've always seen each other as just brothers. Their dynamic has become way more complex than the smart brother/dumb brother dynamic it initially started as. Now they're each other's support, each other's foil, and sometimes each other's antagonist, because siblings.
I also really like the dynamic between best friends Seth and Anna:

I really wanted to depict a straight man and a straight woman who were just friends, acknowledged that the other was attractive (okay, this one's a little more one-sided coughSeththinksAnnaishotcough), but never had any sexual or romantic interest in each other. All too often characters like these wind up falling in love, and that's fine for some, but just not what I'm going for.