What's the best way to use a low durability pitcher like this guy? He has the stamina to start and probably throw 80-90 pitches but with the 14 durability he's not back to 100 for 7-8 days sometimes. I'd like to maximize his innings. Is he doomed to 130 or so a season or is there a better way to use him. Tandem maybe?

https://www.whatifsports.com/hbd/Pages/Popups/PlayerRatings.aspx?pid=12576605

If you want to maximize his innings I'd say you've already done so. 140 innings looks like the limit, as a starter throwing his maximum pitches in a six man rotation.
If you want to maximize his effectiveness, I see you have him set to close right now. Lot of users here don't use closers but I do because it's where I can shield a flawed pitcher and this guy's Pitch ratings aren't great. I'd say you'll get a decent closer out of him but that'll effectively limit his innings.
If I have other good RPs I might try him as a LR1 and set my other LRs to LR2s. First guy out of the bullpen when a starter falters, come in in the 4th or 5th inning and give you three innings max (40 pitch limit or so), hopefully vulture a bunch of wins. But again the number of innings he gets will be situation dependent.

Agree with damag -- closer. However, id do it for different reasons. He's a really good pitcher, but since he has a low health rating, id have him on a low pitch count because I dont want his energy to get really low (higher chance of injury). You might not get the full 130 to 140 IP, but over the long haul, you'll be likely get more IP because he'll likely get injured less often.