Damn, that’s quite a mental tangle you’re in. Let’s unwrap you one step at a time.

“I’ll be living in this weird limbo until his roommate get’s well again.” I disagree. This is clearly an unpleasant situation you’re living with, and it’s not something that can’t be helped. With more consideration and understanding on all sides, things could be much better.

“I know these are legitimate feelings that I have, but I also don’t want to be another burden that he has to deal with.” These certainly are legitimate feelings, and he is your boyfriend. If you don’t take your feelings to him, you’re closing yourself off from him. That can’t be good for your relationship, so don’t do that. They are legitimate feelings and you can talk to him about them, at the very least.

“I’m afraid he’s going to be upset that I would choose to think of myself during this time, and I actually already feel guilty that I do!” Leukemia is a very serious illness, and clearly the roommate is suffering. But just because her suffering is bigger doesn’t mean your suffering isn’t real. Anyone who says, “Well, my problems are worse than yours so you have to shut up,” is unpleasant and inconsiderate, and I’m sure the roommate wouldn’t be like that. I’m sure your boyfriend wouldn’t be like that, either.

“I can’t really ask my S.O. to be there for me during these tough feelings.” As before, talking about tough feelings with your partner is what relationships are for, and what they are sustained by (also by good times, of course). Not talking about them will create distance between you.

“he already has so much on his shoulders.” You’re his girlfriend, though. She’s his roommate. What he’s doing for her in supporting her is great, I support him and it seems you do, too. But being a carer is a tough job, and he may be underestimating the toll it’s taking on him and his relationships with other people. If he had a clearer picture of how his new role as carer is affecting you, he might make different choices. There are other options for him, he can agree with her to have an afternoon ‘off’ every now and then, or ask her to call on her family. He doesn’t actually have to shoulder all of this, and he might see that if someone were to talk to him about it.

“I feel like she relies on him TOO much, but I can’t say that to him.” You can. In fact, you should. It’ll be better for you to air your feelings, better for him to know what’s going on for you and consider ways to change the situation, better for your relationship and better for her to have multiple people to rely on instead of one overworked person. Tell him everything. Tell him you feel guilty. Tell him you feel unhappy that he has no time for you, and how bad you feel for her at the same time. Tell him you feel worried for him because he’s got so much on his shoulders. Tell him you think there are other ways for her to get the help she needs with stuff. Tell him he has a right to his own time, even if his roommate has cancer.

He’s not a bad person if he sits down to talk to her about the care she needs, the care he’s been giving her, and tries to help her find other sources of support. In fact, I think you could say that’s what a smart and caring friend would do.

All the best to all of you.