Tidus not only resembles her past lover, he also claims to be from a place that doesn't exist, makes a first impression through breaking the traditions she looks up to, and Wakka very obviously gives him special treatment for more reasons than one which is not a great start to a pilgrimage where they're supposed to be on their smurfing guard at all times. It doesn't take much suspension of disbelief that she acts the way she does towards him, and while she may snap at him a few times she does overall show a tremendous amount of patience in explaining stuff to him and opens up more and more to giving him the benefit of the doubt especially in Kilika and beyond.

She and Wakka are ultimately very similar overall. Even though Lulu has more experience with Spira overall and has a more open mind - which probably led to Yuna feeling comfortable telling her about her half-heritage - she still absolutely clings to the teachings to cope with the pain and suffering she and the people around her go through. Rather the main difference between them which comes up more than once is that Lulu inclines towards blaming herself, while Wakka tends to blame other people or things, which shows more than anything in how they deal with Chappu's death (although also in other things such as how they deal with Yuna getting repeatedly kidnapped by Al Bhed).

Goddamnit Final Fantasy X has such an amazing cast.