Morinaga is just a normal friend, I don't think she had any romantic feelings for Honda and this may be controversial but I don't think she was introduced to sped up their relationship.
Sakurai is already in love with Honda, that is pretty obvious, Honda is a pretty likeble person, It would be weird if she was alone all the time even though she has friends. So having Morinaga as a new student that wants to be friends with someone be with Honda is pretty reasonable, that happens all the time irl, people like new things, they like new people, it's normal to be really attached to something you like the first days that you have that something in your life.
I don't think the author will use Morinaga just to sped up the relationship, I think she will be a friend to help Sakurai be more honest and Honda be more confident..
This happened to help Sakurai to realize that not always she will be able to depend on Honda asking her favors, If she continued to act the way she was acting, expecting Honda to ask her for a favor, she could get really hurt.
And sakurai isn't using jealousy to strengthen her relationship, she was trying to open up about how she was feeling uneasy to someone she trusts, She feels comfortable enough with Honda now that she can admit how she was missing Honda.
She is just being honest, If she didn't say that Honda probably would feel like Sakurai doesn't care about her.
This just proves how much Sakurai loves Honda now, She feels uneasy seeing Honda being close with someone else. Now, It's not just about the recommendation, it's not just about Honda's desires, Sakurai too wants to be with her.
Thank you so much for the chapter <3<3<3<3