Actually he deserved better as she'd said many times, but that wasn't what he needed to hear right now, And yes Heather did have problems. Managed to shout them from the hills more than anyone ever instead of talking them out but again, not what he needed to hear.
"Sam...I know you don't feel like you're right. Like you're what you are meant to be, and right now, you aren't. But I need you to trust that I'm gonna help you be right. I'm gonna help you feel completely right, maybe for the first time in as long as you can remember. And maybe you'll get some clarity that way"
She believed it with all her heart, believed that she could make him stronger, make him happier with it. She didn't begrudge him love, and if he found the right person she would even be happy for them. But she needed to play her part in his life. Needed him to trust her, because as much as she loved Castiel, Sam was her reason. Sam was the one she would do anything for.
"...Do you want me to help you back upstairs now?" she asked again with a suprising gentleness.