As with any new exercise: start slow and light! I saw only three entries about the ab-roller in your log starting on the 18th. When you felt it "ripping out your mid section", you should have stopped right away. Better would have been to start with caution. Like starting (on knees) with extension limited to where you would feel a good tension (no ripping) for a few reps (best just one) for one set. Then add a rep each day. When you get to 5-10 reps, extend further. When you can do 1 set for 10 reps fully extended you can progress by holding the full extension longer. When you have become good at that, add a second set starting with one rep and building up to 10 reps.
An even more cautious start would be to roll on an inclined board!
Give it a good rest. After a couple of days rest, start these kind of sit ups where your lower legs are on a bench and your upper legs make a 90-degree angle with your lower legs. Don't flex your body and look up to the ceiling. Lift your upper body a couple inches off the floor. Hold that position for a few seconds isometrically. I think you can figure out the reps/set on your own. When your abs are recovered, start using the ab-roller anew with caution.
The ab-roller is a bitch that is easily underestimated. It is not unheard of to tear a muscle when using it. Other injuries (low back, shoulder, pec) are also possible.