How do you guys handle the teenage years when they don't want to visit the ex?

After one year of mandated separation, my divorce will be final this month. Three kids - two are in college and I have one freshman, age 14.

I've maintained full custody the entire year because she can't get him to school or pick him up because of her job. Bus comes to the neighborhood where my house is, not hers.

My son does not like spending time with his Mom because she's trying to force a blended family into him with her BF whose kids are all 7 and under.

I don't want to force him to but I also feel it's good for him to see is Mom even it's only short visits.

Ultimately I need to speak with her and let her know she needs to spend 1 on 1 times.