Dating hella people to catch another guys attention?
It's the same as a kid who pull pranks just to get the attention of its parents. Nikaidou was just hoping that Jun may have a change of heart and start to love her back. Unfortunaly i think that's just make him really worried and wish she found someone for good.
Forcing your love onto someone who already loves another?
Talking about Kurumi ? She don't really force anything since Nikaidou is trying to find someone who can make her forget about Jun. Kurumi know that Jun had already reject Nikaidou and so she probably understand why Nikaidou have dated so much boys. Kurumi is just trying to make Nikaidou stop about this fruitless love.
I feel bad for both childhood friends.
I can understand for Jun but not for Kyou. Kyou never try to confess or make Kurumi understand she love her. You can say Kurumi is dense but it's mostly Kyou's fault on that one.
They should both run away from these toxic MCs.
They can't. They're both too worried about the relation because of Nikaidou frivolous past. Jun want to know if Kurumi is a good person for Nikaidou, as he is worried because of the multiples boyfriends Nikaidou had and how short the relations last each time and Kyou is worried and jealous because she love Kurumi and she is afraid that Nikaidou do the same thing to Kurumi that she does with the boyfriends she had and don't want to see Kurumi sad again.