1.to feel that you belong to a particular group and are accepted by them:
E.G: It's no surprise she's leaving - she never really fitted in.
2.If one thing fits in with another thing, they look pleasant together or are suitable for each other:
E.G: It's a very nice sofa but it doesn't fit in with the rest of the room.
第二種情況:fit sb/sth in (FIND TIME): phrasal verb [M]
to find time to do or deal with something or someone:
E.G: Dr Jones is very busy but I'm sure she'll be able to fit you in tomorrow.
第三種情況:fit in with sth: phrasal verb
If one activity or event fits in with another, they exist or happen together in a way that is convenient.