I adore both of these men so god damn much, its insane how much this game has made me adore its cast...
As for getting Dulrig to 100 Like though, I believe the current cap is 75? He doesn't have more than 1 heart available at the moment, so I imagine they'll up the cap as the relationship progresses in updates, but you can get it to the cap by gifting him Ale.
I'm sure you've noticed, but many items, interactions, etc are capped to stop giving more Like at a certain point - for example, Lube caps at ~40, I believe - but the Ale one changes depending on how much you give him and if you agree to "a quick round" afterwards. You need to have his first heart for the higher numbers though, but that already seems to be covered
To break the 60 cap, you need to give him Ale, and then Share another when prompted - you need multiple in your inventory for this. Then after you Share, you need to agree to "a quick round" with him. The second Ale caps at 70, and the "quick round" caps at 75.
The Wiki covers a lot of things, albeit a bit outdated in areas, so i'd definitely advise looking at it if you're lost!
(My Relationships page with Dulrig for reference)