I agree VDL's words are great
Just to add, make sure you *enjoy* it! If you suffer through every minute of your workouts (even if it's only a 10 min cardio workout), then you are going to have a near impossible time keeping up with it (who wants to make themselves miserable every day?!) and it IS a LIFETIME change... so it's gotta be change you can live with.
Walking is great, try it with a friend, good music, or just watch TV at the gym on the treadmill.
For lifting, start SLOOOOOOWW! You *will* be sore after your first few sessions, (many of us are sore all the time & like it that way, but that's another issue). Go to fatigure (last rep you do in a set of 8-12 reps is the last one you *can* do with good form) & work the muscle till it's tired - not annialited!
Always be sure to have proper form with each exercise. If your form is off, you can not only *not* be working the muscle you're trying to work, you can hurt yourself! You mention your boyfriend has weights, so hopefully he can show you exercises & help you with form/ spot you etc. I would also reccomend not going to fatigue with free weights till you're accostomed to the move & don't risk injury.
As far as diet is concerned, I also think a moderate to gradual approach is best. Day by day, meal by meal, start to take out bad stuff & add in good stuff! Focus on eating closest to nature (fresh fruits & veggies, avoid prepared foods, avoid processed foods like white bread, & processed sugar like sweets) & eating healthy isn't so complex as it may seem!
Good Luck, see you around
-Gladi