He did, after he found out. It's not like I could be like "wow, Thor, haven't seen you since I broke up with you because we were both too busy saving the world to talk to each other and by the way I have cancer."

[ she didn't really want to tell anyone in the first place, least of all someone jane thought she'd left in her past. thor wasn't on earth when she picked up the hammer and by the time he was, the fact that it wasn't helping was already apparent so she didn't ask. she knew what he'd say, because he said it when he asked her to put the hammer down. to give them a chance.

on some level, jane can admit that she wanted to be selfish but the cost benefit analysis just didn't make sense for that. she was already dying. nothing was going to save her, and at least when she was being mighty thor it felt like something was in her control. ]