How about trying to increase in small amounts at a time. Next time you and your running friend go out, warm up with a fast walk, very very slow jog, then walk a minute and start running. Go your 1 1/2 min., walk a minute or two and then try for 1 3/4 min. Do that a couple times and then see if you can go for 2 min.
You never increase your endurance if you don't push yourself - and I don't mean speed, I mean endurance.
I run a slow run or a fast jog - about a 10 min mile - that is a comfortable speed for me. I have gone as far as 9 miles on a TM and done a 10K. I don't think I'll ever get to a Half Marathon - it seems like such a long way, but then you never know.
The "runner's high" usually kicks in for me after a few miles. Then all of a sudden when I am "in the grove", my motion is consistent, my breathing is good (breathing in and then out on my 2nd left step) I can go forever (at least I feel like I could). For me it is a feeling where my legs don't feel tired and my breathing is very comfortable. How you use your arms makes a difference also - don't let them tense up.
If you want some good pointers and running plans, go to
www.runnersworld.com and create a running plan for you and your friend. Try a 5K plan which is 3.1 miles - or 12+ laps around the track.
See what goals you can set and if you can meet them or perhaps even break them.
Best of luck in achieving your goals !