It's hard to be friends with people that make you feel guilty.
Normal guilt, first of all. Talking too much, taking too much. Feeling like you owe someone is hard to get through. To be friends, people require a certain amount of balance. You can pay someone back, talk a little less, listen a little more; but what about when when its deeper than that?
Guilt sometimes springs from hurting people. That's why being in a relationship makes things horrible after the relationship ends. Personally, I hate endings, so I usually try to deny their existence by pretending that feelings and happiness and success grow exponentially and moments amass in strings that go on forever. Who needs an ending when the world just keeps turning around you anyway?
In these instances, however, there are two people that decide how an ending goes. "We can still be friends." Okay, wait and see what the definition of that friendship really is. True platonic care for the other, or subtly avoiding interaction?
Okay, whatever. People are weird. They can have complicated relationships woven out of falsehood and sunshine and chewed gum and paper clips and be extremely happy. So two people, after sharing something beyond secrets, return to being "friends". They see each other and act as if they have never witnessed the the flecks of rare earth metals in each other's eyes and never laid gentle fingertips in the frame of the other's jaw. So what, right?
No. Because there was an ending.
So every time you see this person you associate them with the pain of the ending. It's not necessarily that you even hate this person. (Side note: I don't hate anybody. I am pretty sure that I can sympathize with any human being. I will defend anybody and everybody, because I hurt when other people hurt, as simple as that.) This person just happens to have held you and talked to you and shared in your affections/affectations. But suddenly you can't do that anymore, and that's alright because you agreed that you no longer had any feelings for them anymore, but still, to touch and want to be touched is human, and the last time you touched them is the last time they broke your heart or you broke theirs. It is JUST SIMPLY what it is.
So I think about that mutual touching and mutual pain. For me, all of that is embodied in a lanky boy with a loud voice and animation beyond your wildest dreams. And though he was the one who drew the line and ended it all and broke me in pieces when I was going to end it anyway; I broke him before that. There was a point where I told him that I didn't want to touch, I wanted to talk. And then he sat and stared at his phone until I had to leave.
So I see him and my guilt takes out a trowel and cement and lays a brick wall until I lose my oppertunity to just say Hello. And I see the girl with pretty cheeks and curly hair and the way she glows when he talks to her and I want to say "Be careful. Because he is a sweet little puppy dog and he will chase any bone you throw, but don't forget to speak kindly or he'll think you're mad. Don't forget to walk him so he knows you care. And don't be alarmed if a year later he wants to get back together again, and then ends up with your friend for a month. Don't be alarmed when you don't get mad; because you don't want to kiss him, you just want to smile because he's weird and goofy and he used to make you feel perfect."
Guilt is circumstancial. You can let it build the Great Wall of Not Actual Friendship or you can use it as incentive to make it up to that person. To talk to them and move on with your life. It's that easy. Not as easy as it sounds, but always easier than you think.