assimilate with
To blend harmoniously into a group of people. Do you think he will be able to assimilate with his new class? He can be pretty standoffish. My sister is really outgoing, so she has no trouble assimilating with new people.
assimilate with some people
to join or mix in with people and become accepted by them. It's easy for Karen to assimilate with new people. I want to assimilate rapidly with the other people in my class.