What do i make of this?

It could go two ways. Either she likes gaining and may keep going, or she hates it, and is going to blame you as a bad influence. You'll need to listen and pick up any clues you can, as to which way it is going. In most cases, the best feedees are the ones who are into it no matter what, as opposed to those who try to get into it to please someone.
10 years

When does one become immobile?

There is no way to answer this. It is a combination of age, luck, genes, etc. Young people may be quite mobile at 650 pounds. Someone could injure themselves, and have no problems if they are 120 pounds, but unable to walk if they are 250. It also depends on where the weight is. Someone may be unable to walk because their legs are big and rub together. But if the weight is elsewhere, can walk just fine.
10 years

Sometimes.....

Yes, once you are that weight, you'll never be thin again. If you gain slowly, it won't seem so drastic. You can always stop or delay gaining if it interferes with your life.
10 years

No fat men in my area

There are admirers and fat people anywhere there are people. Probably the best bet is to run an ad. That fat guy who is too embarassed to go out in public may just show up knowing he can be admired.
10 years

I really need your advice :(

I agree with many of the people who say that you had your chance with your old friend. I would tell her that you already have someone. If the relationship with the old friend was meant to be, it will happen anyway. In the meantime, I would not make any major moves until the solution is more obvious.
10 years

New to everything.

There are men who like fat women without requiring them to gain. Some women want to gain. If you don't, then find men who just like fat women the way they are.
10 years

About to give up on site

I really hate the "I'm taking my marbles and going home" posts. (Do people still use that expression?) In addition to what everyone else has said, if you are looking for someone, all it takes is one person. Perhaps that person has not joined yet. You don't need to leave a website. In addition, when you make negative posts, you are probably less likely to find someone, because people are less likely to want to be associated with negative posts.
10 years

Embaressment of being caught

People who are into size positivity would probably disagree that this is a size positive website, because many of the people here do not like their size and want to gain weight.
10 years

Embaressment of being caught

I see your point too, but there is one difference. Large people is a preference, feeding someone, or gaining yourself is considered a fetish. Some people don't want to flaunt their sexual lives, but may not mind flaunting their SO.
10 years

Out to eat with the husband

Time for stretch pants!
10 years