1. *Some* weight gain is normal in a relationship, especially if the girl is taking birth-control pills. However, if the girl refuses to get out and do anything, you have to consider what this implies as the relationship gets more advanced, and I think at some point, it ends. However, my advice would be to sit down and explain all this and to realise that if she doesn't like what she looks like, she will eventually take it out on you, anyway, so best to get that over with.
2. Radical changes in pet behavior come just like radical changes in human behavior: after a traumatic event. Likely as not, the dog was emotionally attatched to the previous boyfriend. The only way to fix this is to spend time with the dog, and encourage any date to do so, as well. This way, you won't have strangers to the dog in the house.
3. Thorny problem, that. It isn't something that a person doing an advice column can really say. It does sound like the parents have a somewhat adversarial relationship with the daughter, so it would seem that not telling is indicated unless the child wishes more verbal abuse. However, that's just my belief.
4. This letter completely fails to indicate whether the bf got her pregnant or not. First things first, get that settled. Second, if you break up with the girl, you're not going to have any control over her. Third, if you expect to be a part of the child's life, expect to pay child support.
My problem with most advice columns is that they tend to pander to what readers want to hear, rather than what people need to do. They don't have nearly enough information to do a decent analysis, yet produce simplistic, canned responses. Oh, well, they seem popular, anyway...
I'm not doing this again; last time no one believed it.