The series have a one huge problem, lack of consistency in characters decisions. This episode shows it painfully. Bellamy decision is contradiction to what he did and worked for in last twenty episodes, betrayal to his sister and Lincoln and his tribe, Clarke and actually everyone who trusted him. Things like that are just annoying. But we saw it already too many times in the show. From criminal and anarchist who doesn't care about anyone but himself to reasonable leader when it comes to Bellamy. From reasonable leader to a religious fanatic like Thelonius. From selfless pacifist to a cold blooded murderer in case of Finn and from egoistical killer and maniac to helpful team member and voice of reason in case of John Murphy, from power hungry, ruthless security officer to a sensible diplomat - Kane. It really becomes very annoying in longer term i do know people change but does they really change so often and so drastically? From the beginning of the show i have a feeling that producers didn't hired enough actors. All of plot shifts and surprises they have for us would be a lot more reasonable if they used twice as many people to introduce them. Instead they are using the same characters to do things that are completely contrary for them. And this episode is painful reminder. Bellamy actions are complete contradicion to his character but could fit another member of original hundred that we didn't had too many chances to know yet, resulting with the same outcome. Everything would be reasonable and well written then. Now it's just another bad plot twist and character change that doesn't make any sense especially that his action should most probably get Clarke killed, alienate Octavia forever (maybe even result in her death if she choose to eg. warn Grounders and/or escape with Lincoln) and result in hundreds other deaths, Sky Crew also. Whole scenario from the beginning is full of such bad character changes and i have strong feeling that script was written for a lot of more characters but it's played by very limited actor crew.
In the end i have a theory that original scripts included more characters that take lead roles in various episodes and maybe die along the way or goes into backstage for some time (just as Game of Thrones and Walking Dead were not afraid to kill their characters), but instead producers decided that audience already like first crew so they shouldn't do any bold moves with the show and rewritten the script to save all twists but performed by half of the planned crew. Bad decision.