In the series The 100, we first see main character Clarke falling in love with Finn but the show season ends with her odd interaction towards the female Lexa. So is she really bisexual?
Yes, she is. This has been confirmed by the show's co-writers on several occasions:
AfterEllen.com: Were you part of creating the Clexa relationship?
Kira Snyder: The stories are all collaboratively written. Lexa was introduced in the episode that I wrote. It just happened to be where I came up in the writing assignment series. It was something we talked about and [creator] Jason Rothenberg was supportive of and the CW was supportive of so we’re really happy to have that storyline and really gratified that it’s sparked the fan response and press response that it has. It just goes down to the issues of representation and seeing [bisexual] people on screen. But that’ something I’m very pleased to be involved with.
AE: Do you see Clarke as bisexual?
KS: I believe, yes, officially Clarke is bisexual.
And per twitter:
@JRothenbergTV - Clarke is a bisexual character. Remember that in this society, no one’s worried about it. They’re worried about spears to the chest.
She is. The showrunner, writers and actors confirmed it on several occasions, last time at this year's San Diego Comic-Con I think.