why bestemme meg - why can one not just say bestemme? Below(above?) it states,
Å bestemme seg for = to decide (up)on for yourself
so is it said bestemme meg to clarify to whom the decision belongs and if so why is it not possessive - why not bestemme min
I think what is really confusing me is how would you just say "I've decided" or "I've made up my mind" without referring to a specific decision?
Is the definition of bestemme closer to 'determination' or 'conclusion'?
"Å bestemme seg" is a reflexive verb when you're making the decision on your own behalf, particularly so when lacking another object (the decision itself). It can also be reflexive when the decision is specified, but the option of leaving out the reflexive pronoun would then be open to you. When translating it to English, you leave out the reflexive pronoun regardless, as "to decide" is not a reflexive verb.
The reflexive pronoun is not there to stress that it's the person in question who's made the decision (though they have done so), it's there as a part of the verb. If you do want to stress that you've made your own decision, you could add "selv": "Jeg har bestemt det selv" ("I've decided it/so myself.")
"Jeg har bestemt meg." is the sentence you're looking for.
Jeg må bestemme meg for en kandidat jeg kommer til å støtte.
Å bestemme seg for = to decide (up)on for yourself. Used as a reflexive verb the preposition "for" belongs in the phrase.
However it doesn't sound quite natural, I had to chew on this as I initially felt it was the mix of verb forms. "Kommer til å" is a future obligation of something already decided (ie a declaration, "I'm going to leave early today", jeg kommer til å dra tidlig i dag), while "må bestemme meg" is a present time obligation to make the decision, having them in the same sentence makes my brain stumble. I'd substitute "kommer til å" with either "skal/vil".
The other objection I have is that you wouldn't say "en kandidat" in this sentence, but "hvilken kandidat". Which/what candidate. If you skip the going to-part, "en kandidat" sounds fine.
Jeg må bestemme meg for hvilken kandidat jeg skal/vil støtte. Jeg må bestemme meg for en kandidat.
Jeg kommer til å støtte en kandidat, jeg må (bare) bestemme meg for hvilken. "I'm going to support a candidate, I (just) have to decide which one."
Jeg har bestemt meg for hvilken kandidat jeg kommer til å støtte. "I have decided which candidate I'm going to support. "