Should I feel ashamed if I ask my friend to pay his/her part?

Ok folks,here’s the story;
I usually pay for my friend if I ask him/her (a ‘him’ usually insist to pay for our food)to go out to eat with me,I really like to invite my friend to eat together somewhere else so we can talk about interesting thing/or to know each other better but I don’t always have much money for constant feast invitation and I feel that I’ve been used since I always pay for our food and I suspect that the reason she(and other friends,we usually go as duo/trio) wants to go to eat with me because I offer “free food” for her. I feel guilty since I’m the one who invite her and I’m the one who suggest that I should pay for our food.

My SO usually the one who pay for me if he invites me to eat outside and for other entertainments but sometime I pay for him in return.

Can someone here know what’s the best solution in this situation? I really want that we pay equally for our part if I invite someone with me.
Even if there is a solution,don’t you think it would be awkward if I suddenly ask each of us to pay for our own since I have been paying for them from along time ago.