All of this sounds rather innocent... except one REALLY BIG RED FLAG.
These four words change the whole situation
sometimes when I am alone with [the housemate] he will ask [for] a hug.
Hugging without your boyfriend present is a really big problem - it is not "just hugging".
You are right to feel weird about this.
You don't say that this only happens when your boyfriend is not there, so I assume sometimes he is there - but my advice would be the same if that's wrong.
Can anyone offer any advice for this situation?
Yes - you need to firmly stand up for yourself before something happens
The first person you need to address this with is your boyfriend1
I don't know if you are aware of this but [roommate] is asking me for hugs when you aren't around.
At first it seemed harmless, and I just wanted to be nice.
However, it is making me increasingly uncomfortable.
Can you explain to him that I am not a hugger? I'm not going to hug him anymore. I think it would soften the blow if you explain that I'm not a hugger before it comes up again.
Boyfriend should take this seriously.
If he acts hesitant, make it clear how important this is to you. Look him in the eye and say, "I need your support on this," and wait.
Don't use the word please when you say this - that would send the wrong message (that he has the option to not support you on this).
Then boyfriend needs to talk to roommate - something like:
[OP] really isn't much of a hugger. She is a nice person and sometimes accommodates people she likes.
As the hugging has continued it has made her increasingly uncomfortable, because, like I said, she isn't much of a hugger. Anyway she isn't going to hug you any more please don't ask her again.
Boyfriend should address this with roommate when you are not present.
Don't go over again until your boyfriend confirms he has had this conversation with roommate.
Your response to another hug request should be, "Oh, I thought that boyfriend was going to talk to you about that. I'm not much of a hugger." DON'T hug him again for any reason (not even if he cries about it).
IF the next time you see roommate he apologizes for making you feel uncomfortable, AND never asks for another hug - there wasn't a problem.
IF roommate asks for another hug2 (maybe weeks from now "oh, sorry I forgot" no he didn't) then I'd say you cut this off at the pass before he did something.
You shouldn't be alone with him if he asks for another hug.
(If you are worried that your boyfriend wasn't firm, or was misunderstood you have the option of ignoring it once.)
Having him act ask your intermediary softens the blow.
He knows the roommate better than you, is the one that needs to live with the guy.
It less awkward because you aren't present, gives roommate time to process and discuss.
FWIW if I were the boyfriend in this situation I would want to know about it.
OP could do this herself... but remember that she is worried about causing offense.
2 Unless dementia is involved (and you don't mention this) his asking for another hug means that he is not respecting your boundaries.
If you say, "No hugs" then he should respect that.
You do not have to hug anyone you don't want to - whether you have a previous pattern of hugging them or not - NOTHING trumps this fact neither his disability nor anything else!