Never let someone be the reason for your death. Never allow someone to make you consider killing yourself. You are the most valuable person to yourself. You do not need to depend on anyone's love for you for your own happiness. Life is breathtaking when you are in love with yourself. To have a person is something that should come after. And even so, that person should not dictate your happiness. I think if you are really ready for such an emotional relationship, you will realize that that person only serves to add more happiness than you thought possible. They shouldn't be bringing you down so hard like this. Please consider getting away from them as soon as possible if they are causing you to feel depressed and suicidal. It's a sign.
I wish you the best of luck in couples counselling and I'm proud of you for acting to make things better. Mental illnesses are not fun, and tension in relationships don't help. I hope you have the courage to do whatever you can to help yourself. Always put yourself first. And please, keep on living. You can do this. There are better things to come.
No one will /always/ make you happy. People's feelings are inescapably complex; sometimes we crave a different sort of happiness than such as we get from a particular someone, and sometimes this someone will do things, driven by their own complex feelings, that don't align with their habits and actions that usually please you. This is not necessarily either your fault or theirs and doesn't automatically condemn the relationship. If they're bringing happiness to your life in larger quantities than any hurt that they will inexplicably and unintentionally cause, and letting them go would bring you more pain than it would relief, hold onto them. Don't settle for dissatisfaction, but don't search for perfection, either.