Steve:
He stays over at your place. You being upset is one of the reasons that Steve will stay with you, because he knows that you feel better when you sleep with him there. Also he wants to be there for you and this way he can be, literally.
Bucky:
All of the cuddles. When you're upset Bucky won't leave you alone for a second, and he'll curl up with you on the couch or the bed. He holds you closely, letting his warmth and contact help you feel better. Eventually the love he insists upon showing you rubs off and you will start to feel better.
Pietro:
He takes you to your secret lab. There you two can be alone together and have all the time in the world to talk about what's bothering you. At first you won't want to talk about it, but eventually those big puppy dog eyes of Pietro's will wear you down. You will let it all out and he'll listen to every word.
Loki:
He takes you star gazing. He knows that it's something you love and looking at other worlds can be a nice distraction from your own. It's a good excuse to cuddle with him and he makes you feel better by comparing your eyes to the stars. Usually you will fall asleep staring up at the sky and you will wake the next day to find Loki had carried you to bed, which makes you even happier.
Clint:
He takes you to the range. You haven't been shooting long, but Clint knows it's a great way to get out the tough emotions. He'll shoot with you for hours until whatever's bothering you starts to fade away and you're ready to talk about it. Also spending that much time with him helps too.
Thor:
He goes running with you. Thor knows that running is a good way for you to deal with multiple negative emotions, even though you have a hard time getting yourself to go out when you're upset. Thor basically drags you out because he knows you will feel better afterwards and he goes with you to keep you company. You do end up feeling better and you enjoy the company.
Tony:
He makes you breakfast. It doesn't matter if it's the morning, middle of the day , or even the middle of the night. He will drag you to the kitchen to cook for you, and breakfast foods are really the only things he can cook. It may not be the best food in the world, but you appreciate the effort and it's cute watching him cook.
Natasha:
Living room dancing. Natasha will move the coffee table so that there's more room in the center of the room. Then she will turn on some slow music and dance with you until you start feeling a little better. Then she will turn on some faster music and will start to dance ridiculously with you, both of you laughing at one another.
Wanda:
Home ice cream date. Wanda will buy you your favorite ice cream and some for herself and bring them home. Then she will serve you both some and drag you to the couch and you make you sit and eat with her. Once you've both finished she will encourage you to talk things over with her.
A/N Sorry Tony's isn't better.