Well, as far as I know, stretch marks come from the gaining process, not the losing process, so if you're losing hopefully you won't develop too many - if you want to use some lotion on them, it certainly won't hurt anything. I'm fairly young (28) and I've had very minimal problems with loose skin after losing over 50 lbs. - there's a small amount on my stomach, but that's about it.
I'd say the oddest side-effect for me has been this -after losing a good amount of weight (maybe 35 lbs. or so) - every day that I wasn't perfectly on plan, I started to think I'd see the old 200+ lb. me in the mirror when I woke up in the morning. I don't think it was necessarily that I had a warped body image, but I guess I WAS over-emphasizing mistakes and giving into the fear that I'd let myself get to a size I hated again.
Of course, the old me is never in the mirror, even if I down a whole pizza the night before
But that fear is still there every time I have a cheat day, and I imagine it's going to take a long time before I completely accept all of the hard work I'm doing to change my health and size. Most of the time, if I'm having that fear, I make myself go put on my old size 20 jeans and see how they're falling off of me now. Then I *know* I'm not that big!
With my relationship, I'm lucky to have a family and BF that have been nothing but supportive, so I've had to deal with very little "sabotage" - however, talking to people who've gone through it in a lot of different circumstances might lend perspective to your own life
Female, 30 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 8/30/13 = 179.8 (net: -35.4)
Current mini-goal: 175 lbs.
Lowest weight: 156.7 lbs.
150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130 lbs.
"You don't have to change your life today. You only need to change your day today."