As the title states, i can't recruit other companions after completing the whole quest line. I tried getting Boone again while having Veronica with me, but he keeps saying that i already have 2 companions which i don't. Tried going back to Primm to recruit ed-e and asking him to leave, then went back to Boone again. Didn't work. Am i doing something wrongly? or is this a bug?

You can only have 1 human companion at a time. If you want Veronice, you need to tell Boone to leave. Afaik you can have Rex or ED + one human compaion at any time. Once I got a base at the Casino I just park companions there and swap them out as I want.