Can you help me give relationship advice to my younger sister?

Yeah, yeah, TL;DR.

My little sister (she is twenty-two) is living with a boyfriend of two years. They’re living next door to her parents, having just moved into their own place a few months ago.

Recently, she’s opened up to me through texts that she is unhappy in the relationship. They have fundamental differences in their expectations of the future – she wants children, he doesn’t – and they have incompatible sex drives. She’s upset at the lack of physical affection in their relationship. She feels he’s more interested in his “toys” than in her.

Originally, I encouraged her to talk to him, to make known her issues and go from there. When she did bring up the fact that she feels she needs more affection – “Just to be held sometimes” – his response was that it’s not going to happen because it’s not something he’s ever liked doing, and it’s not that he doesn’t love her, because they’re like best friends.

She knows the relationship is over. She has told me she “loves being with him” but doesn’t know that she’s in love.

I asked her what she would say if her best friend came to her saying her boyfriend was unaffectionate, didn’t want children, and was uninterested in sex. Her response was “Damn. :-(”

She is worried that if she breaks up with him, that it will break his heart. And she doesn’t want to hurt him. Meanwhile, she’s in a relationship that’s dooming her to unhappiness.

She is asking me what she should do, or what she should say. Frankly, I’m not very good at the whole “feelings” thing – I never learned to understand my own, much less understand someone else’s enough to inform their actions. I’ve given her all the logic I could – “If you’re not in love with him, why would you be willing to give up the chance to be a mother for him?” “Your happiness should be more important to you, because you have to live your life, not him”.

But it’s not what she needs. She isn’t thinking rationally, so rational suggestions aren’t helping.

Help?