I don't think they necessarily "didn't want to do anything with each other" in the beginning, well Gamora definitely seemed to resent that she got stuck with this group, she called them the "biggest idiots in the galaxy", she definitely acted cold towards them in the beginning. But I don't think Peter necessarily felt the same way about Gamora, I mean sure they fought each other over the orb containing the power stone when they first met each other, but I think by the time they first met, Peter was already fascinated by Gamora and throughout the first movie he tried to woo her and win her affections, and he continued to do so in GOTG2. So I get the impression that Peter never disliked Gamora, he was always fascinated by her from the very beginning and he fell in love with her very quickly. It just took longer for Gamora to feel the same way about Peter.