QUestion on joining the legion/not joining the legion?

[Xiola]

I am quite far into the main story. SOmewhere not long after the Ostrich killing mission, I had to go to Blacky to further the main quest and he said something like 'take them all down right now'.

Because I had to restock on ammo and stuff, and also just to see what the other options were I asked and he said 'go and see the legion commander'.

SO I said 'OK'.

The Legion guy said I must join the legion. I thought, no thanks and went back to Blacky, but even tho I said 'no' to the legion, Blacky now he acts as if I have joined the legion and there is no option for 'his way' of the main quest.

Do I HAVE to join the legion? Or have I just missed the opportunity to do it blackys way by simply asking 'is there another way?'

What are the differences if I joint he legion or not? Have I gone down a bad path? SHould I reload a much earlier save just to do it 'blackys way'?

Thanks in advance guys for putting up with all the questions