When they kiss for the first time she's almost glad she's being shot at by the Collectors right after.
Garrus Vakarian is great in bed- but he is a Turian. His skin is tough as it runs along hers, his positions are from an entirely different world, and his biology makes her skin break out in hives. Turians don't 'kiss', they usually bite at one another's mandibles for foreplay. But he humors her human customs and kisses her- and it's not so bad. The rough flaps of his mouth are actually sensual against her soft lips, so kissing is translatable to their every day lives. It's just the saliva that upsets her stomach.
She's not sure how a Turian baby would work if natural sex makes her feel like she's got the worst cramps of her life. His 'genetic material' irritates the hell out of her uterine lining, and she was fairly certain his mysterious tendency towards illness was because he happened to bite her. It was certainly why her body was breaking out in hives around the area.
But discomfort never seems to stop her. Neither does the fact that their shared fridge has to be color coded so they don't kill each other with the wrong food. She has gotten used to it. And it's even amusing to make a dextro meal just for him and see his surprise when it's been given human style touches.
Marriage isn't even the same for them. They have a system of monogamy, but it's hardly comparable to human marriage which is based deeply in love. Duty is king for Turians. If you marry, marry someone you feel committed to. Love is entirely possible and not terribly uncommon, but it's not the same. Garrus still struggles to say that he loves her, because it is not what Turians are raised to do. You care for people. You aren't raised in schools until you're 18 and given a choice for whatever you want. You are sent to boot camp. Men. Women. It's the same.
There's so much standing in the way of this cross species liaison.
Garrus is completely puzzled at the concept of sexism for women. How was humanity still working on the glass ceiling when it's hero was a woman?
“I wasn't given any respect until Akuze- and you can't walk out of 50 men dying and taking down a Thresher Maw without getting a little respect,” and Shepard proceeded to explain the issues in military, how just 100 years ago acts had to be enacted to protect women from rape in the military. Turians don't fail to punish those who are incorrect. A rapist confronted usually confesses, and is always harshly punished. A human woman is still given side looks of “are you sure you didn't ask for it?” by members of their species.
Turians value the whole. Humans value the self. Well, most humans. The unfortunate end of migrating into space was humanity was beginning to lose a lot of it's variation- everyone wanted to catch up with the 'big space kids' and so they did the human thing and conformed and adapted. This meant more popular western idealizations of self began to spread. So to humans Shepard was the best case, to Turians Shepard was just a lucky draw. Very, very lucky.
Their relationship by all accounts should be nearly impossible.
But Shepard instead looks to her hives as they go down and her cramps as they subside and she laughs.
“Getting better than it used to be,” she says as she puts on her jacket. Because this isn't the worst she's ever dealt with, and it's certainly got a better pay off.
And on his side of the bed at night Garrus ignores the itching on his skin from her fluids and concludes exactly the same thing. It might be hard, but that never stops either of them. It simply reminds them how much its worth it in the end.
So he drapes his awkwardly rough arm around the soft flesh of her skin and smiles the way she can barely recognize, because she found a way to make this happen when it seemed impossible.
And that is all they need.