Son's dad thinks I pay the babysitter too much

Me and my son's dad aren't together. He is behind on child support and not working. He calls our son here and there but mostly a deadbeat. My son is 9 with a lot of behavioral problems. He's gotten suspended from school several times and kicked out of aftercare. I was worried to lose my job ex wouldn't help. I hired a teenager to babysit and honestly my son loves him. He has actually helped my son improve his behavior. He's babysitting this weekend. My ex asked how much I usually pay him. I usually pay him 50/day during the week so $250 in total a week. My ex says that's too much. Especially since I always order him and my son dinner and sometimes I have soda that he likes in the fridge. I'm just really thankful because nobody would watch my son and he's helped with his behavior. My ex was saying that's too much and accused me of doing it because I'm attracted to a 17 year old. I'm 28. No I'm not attracted to my son's teenage babysitter. He's making me feel bad and like I'm a weirdo for being grateful.

Edit: He only watches my son about 3 hours.