offered a shared role but not with the person I expected

[pleasenotmondayagain]

A restructuring process at work means that a new management position has been created. Two groups are being merged, a handful of additional staff are joining, and a handful of other people in my current group are moving elsewhere in the same organisation. I'm currently group 'A', but I've been working quite closely with a colleague in group 'B' on a couple of projects and that has gone well. We applied for the new position, but we both suggested in our applications that having someone from each group sharing the management position would be a good thing and that we would be willing to share the role.

Interviews were yesterday. I was invited to a meeting with one of the more senior members of the company this afternoon, and offered the job. Apparently they liked my application, and they also liked the idea of having both group A and group B represented in the transition period. But they don't want to offer half the job to my colleague from group B - they have someone else in mind.

There is nothing in writing yet, but I assume that the other person will accept the role. I'm not sure what to do.

I feel guilty about accepting the job without my co-applicant, although she knows the situation, and has been very nice about it.
I know the person who I'll be working with and I really don't know if we'll be able to work together. That's not just loyalty to my colleague. The other person has a very different style (shouty), personality, attitude, whatever you call it. Maybe that's a good thing, but it does worry me.
I could just withdraw my application. The job looked interesting, good experience etc etc, but my current job is enjoyable.
I could say that I am willing to accept the new position, but not to share it. I don't know if that's possible to argue that I was willing to share with person A, but not anyone else.
I could take the shared role, and if it doesn't work, try to resign from it, assuming my current job is something I can go back to.

I assume that the only option over which I have full control is a decision to withdraw my application. Either that, or hope that the other person appointed is repulsed by the thought of working with me and is currently planning to leave the country. Perhaps I need to develop some hideous belching, farting, loud whistling habit in the office (not really a mature way to behave, but fun to imagine.I could take lessons from DH)

I'd accept the role and not have your own career aspirations stunted by this other person. Nothing ventured nothing gained. Don't jump to the automatic conclusion they'll make life difficult for you, they may surprise you.

It's a lesson in corporate life - the ability to work effectively with someone who isn't your cup of tea. You will learn far more from that experience than from working with a "mate". And it's a scenario you could use at future interviews " talk about a time you had to work with a difficult person and how you dealt with it"

Take the role. You have no reason to feel guilty - this isn't a situation you have engineered. I definitely don't think you should say you were only willing to share with person A, as that will make you sound immature (not saying you are, but that's how it could come across). I agree with pp that working with someone who is very different from you will be a good experience, and good for your CV.

Two replies that say exactly what I didn't want to hear! But only because I know that you are right. There is no need to feel guilty, and I appreciate the the employer works on the basis of best fit rather than best friends.
DH pointed out this morning that there is every chance that my job partner will be groaning inwardly about the prospect of working with me. We may surprise each other.
I don't know if I'm meant to accept the role and then discuss how we work together, or have the discussion then agree the contract. Either way, I should try to see this as a good situation.