Varies.
One of the girls has a boyfriend when she starts kinda seeing the OP, flirting at least.
One of the girls is bi and can start something up with the gym trainer. If you encourage that relationship you end up in a 3 way which has one of the best endings where both girls end up in love with the MC and having his babies. If you fuck up at any time, specifically one choice in the cinema near the end, they will both leave the MC at the end.
MC can start a relationship with the teacher and cheat on her with her friend. If you do that she breaks things off with you.
MC can also cheat on one of the other LI's which also causes a breakup.
MC can start a relationship with the blonde who works with him in the law firm. She's married and will leave her husband for the MC if you carry on with her route.
You can cheat on your room mate if you start seeing her with her "friend" that comes to visit. That will end the relationship.
Basically it's a date sim, you can cheat but if you try and date multiple women it will end badly.