Prefacing with while I don't read poly stories, that does not mean I find anything morally wrong with them. I just prefer to read love stories between two people. Now, I see Len as being as very possessive over someone he was in love. I struggle to imagine him being ok with sharing his lover. Do you think there are canonical clues that prove he'd be into a serious poly relationship? My inability to see Lenlike that could very easily just be not having a strong understanding of poly relationships
I think this is one of those things that our personal experiences and identities mean we see what we want (or don’t) want to see in a character and narrative? Which is great! It allows us to identify with characters and see ourselves in them and gain meaning from stories. But it also means we can take the same signs, symbols, actions, and stories - and come away with really different interpretations of them, all of which are valid.
Because I absolutely think Len would be okay with a serious poly relationship, but don’t have any clues at all from canon to back that up. We barely have clues from canon to back up the fact that he’d be okay with a relationship at all, and the only clue we do have is one scene between him and Sara in Legends where he talks about envisioning a future with her. Up till late Legends S1, I actually thought the most close reading of canon would have been an aromantic Len...
And the thing about “would Len be open to poly” is that a lot of the time, you can’t tell if someone would be poly on the surface? I don’t think there are always obvious “signs” or anything like that, short of seeing that person in a relationship and their relationship structure, or else them talking about it and their feelings related to relationships, openness, jealousy etc.
We interpret Len as possessive (or I do, at least) but we don’t have much from canon to support that except how controlling he is over Mick, and how put out he is when The Flash doesn’t direct attention his way.
Would that translate into a relationship? An unhealthily controlling relationship (like he sometimes has with Mick) is a problem regardless, and I’d honestly hope that whoever Len was in a relationship with, he’d learn to trust them a bit more than that.
Would he be jealous? Possibly. But he might also find a poly structure works better for him because there could be (not saying this is true for all poly relationships, just is possible in some) less pressure to fill his partner’s needs and to be “on” all the time for a partner, and would be able to maintain more of his own time and space if he were ‘sharing’ his partner. He might also feel less tied down by monogamy and less like he’s likely to fuck up and ruin something, if he’s not carrying 50% of the weight of making it work (which is a little ironic because to make poly work, people typically have to communicate even better with their partner(s), but it might curtail Len’s self-sabotaging instincts a bit).
It’s also likely that a lot of his past encounters haven’t been in serious monogamous relationships, so he might not have a strong basis for wanting/expecting monogamy and might prefer a certain degree of openness?
But it’s also possible that the opposite is true for all of these - that he would be possessive and that “sharing” might make him feel less like the focus of his partner’s attention, and might make him insecure. Without having many (any?) serious monogamous relationships, he might crave being someone’s sole focus and single partner and might not feel comfortable in a more open or poly relationship where he doesn’t get that sole connection from a partner.
I can’t think offhand of any canonical evidence for one or the other, though others might try to make arguments in favor of one either way. But I really think it’s one of those things where we get the joy of figuring out what works best for us in terms of interpreting a character, and making that our headcanon or reading fic that fits that interpretation.