Seriously???? What's the difference at this point? I get that he never wanted to get married before but we all knew MC wanted to - he even talked about it a couple of times (he even tried to make Kotani jealous by saying he might marry the other Alpha if they hit it off). Kotani should have brought it up way before this (he knew that MC had a marriage meeting with that other Alpha).
My guess - ML was happy to see MC again (since it's been a while) and knew he'd been drinking so was hoping to maybe get a little more flirting/something more from ML, that's why he was slightly disappointed when ML said he'd only had a little to drink. ML needs to stop leading MC on - they clearly like each other, don't know why ML keeps messing with MC like this.