Another thread that takes in interesting course! I'm late to the party, nonetheless some comments:
Assuming on all 3 situation he was out drinking with his friends:
your boyfriend should drink less and study more.
One important bit of information is missing: do you give any financial or material support to him?
Your English is ok for posting on this forum, but not for teaching.
You could ask your boyfriend to quit excessive drinking and hanging out with his friends, but he will probably choose alcohol and friends over you.
When I search for way from Chiang Mai to Doi Saket on google maps, it chooses a point about 9 km south of the center of the old town as "Chiang Mai", and then gives the distances you quoted. (I could already see from "Route 121 and Route 1014" that there must be something wrong, as this is not the shortest way from CM to Doi Saket).
However if I go from Wat Chedi Luang Worawihan (about center of Chiang Mai old town) to Wat Phra That Doi Saket (about center of Doi Saket) I get "43 min (22.2 km) via Route 118" which is close to the OP's numbers. And Central Festival is NE of CM, that means closer to Doi Saket. Anyway, I wouldn't argue about "15-20 km" versus 28 km.
Love it how a post about relationship problems turns into intricacies of Thai geography!
Even if the op's numbers are correct here, I wouldn't be surprised if he turned out to be a troll, as the rest of the story is fishy. But then, when I started posting, I was accused of being a troll, so I give the benefit of doubt.
Apart from the occasions where I know better than fountainhall when it come to gay saunas in Thailand or intricacies of Thai geography, I bow to his experience and knowledge in all things South-East Asian, and especially thank for advice on Taipei, a place I would not have gone to if it hadn't been for fountainhall's reports on the forums. Whoever suggests fountainhall go out more must have missed all those excellent trip reports.