Feelings, there are happy, sad, angry, anxious, depress, guilty and many more. These feelings are the existence in human relationships. Therefore no one should question why such feelings occurred.
I could say that I've experienced mostly an angry feeling rather than being happy. It's just that I'm literally always angry at myself. Why? Because whatever I do will somehow looks wrong to others. For example, I did my best in a competition although I lost, is it my fault? Shouldn't it be that my opponent is better than me or even his/her chance of winning that time was higher? Think of it in both ways.
Another example nowadays, boys and girls, men and women, they kept fighting back with each other using the social media. "All guys are these, all women are that bla bla bla...", to me, both genders have their own personality and feelings. Women are soft and vulnerable yet dedicated whereas men are tough and could also be soft at some situation. What I'm trying to say here is I'm quite annoyed with both genders accusing and assuming each other. Both genders could cheat, lie, stay loyal, be generous, be hopelessly romantic and so on, not only based on one gender. There are reasons for some people who became that way.
But then again, if you're rasional and mature enough, you should know that no matter how many times your heart has been broken, you've been cheated on or lied to, you CAN move on and make better choices for your life. Change yourself for the better. If you're still aching with your past relationship, think of how your parents felt, your God felt then when you don't fulfill your duty to them. Don't let strangers with memories crushes you and your future. There are still a lot more to go through and I'm sure that all of you are strong enough to make it. Fighting!