its supposed to be a new women. I believe after she dies he eventually moves. But he is greatful to Kuriumi for the love and growth they had together. I think he believes he became a great man because of her. It honestly isnt clear she dies or not, but I think she dies of her disease

Although she had died but she is still with Aiba. If you read the last page, last column. You will find Aiba and her conversation.

Aiba: Hey
Kurumi (Ghost form - invisiable): Yeah?
Aiba: On second thought
Aiba: About that golden shower...

Correct me if i'm wrong.
http://3.p.s.mhcdn.net/store/manga/3412/08-076.0/compressed/ e076_30.jpg

My theory is that she is Kurumi's sister. It's reaaaaally hard to imagine Hideo falling in love with anyone after the experience with Kurumi, unless it was a person very similar to her, in this case her sister.

Kurumi mentions having siblings at one point in the story, so we know for sure that she has a sibling. As they are traveling by the Children's Home on the train, Kurumi waves subtly as to say goodbye (which implies that she knows the place and suggests she was fostered at an early age). Then, the young women there who looks very similar to Kurumi says something like "Is Kurumi here? I thought I smelled her.." which implies that she obviously knows Kurumi somehow from before she moved to the city, and because she says "I thought I smelled her.." it's extremely likely that she is very close to Kurumi and knows her 'scent' essentially, so it's practically confirmed that this is Kurumi's sister. The older woman is probably the woman who raised Kurumi and her sister, and he sister stuck around to help with the children's home.

Why I think the woman at the end with Hideo is the same person is mainly just based on what I said before, I can't fathom him getting over the experience with Kurumi and being able to move on to another woman, so it must be her sister, or something. He probably doesn't know it's her, but the reason he loves her is because she reminds him so much of Kurumi. Plus, she looks exactly like an aged version of what Kurumi's sister at the children's home would probably look like, so I think that's what's intended here.

I think MrToaster56 is 100 percent correct. His theory explains the two main mysteries about the ending: Who is that woman he's seen with at the end?
and
Why that little scene with her family?
There's no reason in the story for that family scene to appear except to help explain the end. I'm glad to have this manga explained in a way that is happy. This author had been too competent and professional, throughout all those volume, to put in meaningless scenes, so I wouldn't expect him to do it for the first time at the very end.

I cried at the end because death for the great girl heroine was such a loss, and because there was really no remnant of her left except his memory. If he married her sister, part of what he'd loved would most likely still be in his life.

I disagree. The women on the end had a mole on her chin. The sister wasnt shown to have. I think that he moved on and kurumi died at the sea. I also think that they dint have sex because of the line "when i wake up, lets have sex."

they most definitely didn't have sex at the end before she died because she was an assassin sent by the OB network to try to break him. assuming the OB has ways of knowing, and seeing as how he's becoming a doctor [or became? i forget] he succeeded in staying a virgin the entire time until he graduated and his future was guaranteed to be secured. another reason why i think she was an assassin was some hints here and there early on, and the doctor being an OB was too much of a coincidence - also i believe she agreed to it so the OB network can help pay for her apartment and hospital fees.