A day before Tuesday is Monday. A day after Tuesday is Wednesday.
The day Tuesday comes after Monday. The day Tuesday comes after Monday.
The day that comes between Monday and Tuesday is, in fact, Tuesday. However, if you're considering the context of a week, Monday is followed directly by Tuesday without any intervening days. Thus, there is no day that specifically comes between them.
Thursday is two days after Tuesday.
Monday.
Tuesday.
Wednesday comes after Tuesday and before Thursday.
Tuesday comes 2 days after Sunday. This is just the way the calendar has been set up.
Tuesday
Sunday
Wednesday comes after Tuesday and before Thursday.
Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.Tuesday.
Um... No... It's a day... That comes after Monday...