I had a track coach once who, when I told him I was getting shin splints, told me, "Well, if you were a guy, I'd tell you to tough it out, but maybe you'd better take it easy for a few days." I'll give you the same advice. You'll probably take it the same way I did.
Have a good hike. I don't think you'll slow anybody down.
Seriously, though, you don't have time to change your weight that much between now and then. Your hiking partner knew what you weighed when you set the hike up, didn't he? Maybe he doesn't
want a forced march.
You have time to change your outlook, and you have time to get in enough hikes to ascertain whether you are going to enjoy the proposed outing. Go get some miles in (which always helps me eat healthier, as a side issue) and if you still don't think it is going to be fun, then report your findings to your fellow hiker and re-schedule something else more appropriate if you need to. If nothing else, he'll reassure you about what his expectations are, if you talk about it. You're always going to be a lot worse and a lot better than somebody else out there. Don't beat yourself up about that. Life is too short.
If you decide to do it, though, then decide to do it, and decide to enjoy it. Be a buckaroo. If you do that, nobody is going to be down on you for doing your best, making the best of it, and being a good time to be around. That is probably all he ever expected in the first place.
I've found the needy thing is sometimes a separate issue. I'll start feeling needy, and then find myself looking for something to feel needy about. If you think you're doing that, you don't have to drag the hike into it. Go find a friend and tell them, "I'm feeling needy. Let's go do something fun. You spend the whole time telling me how wonderful I am. I'll buy and I'll owe you one." Sometimes, that helps.
Good luck! Hope you're feeling better tomorrow.