I need advice please

I'm worried about my boyfriend. He does this thing where he binge eats whatever he wants whenever he wants until he's slightly overweight. But then when he realises he's over weight rather than eating healthy or working out he just stops eating. I have to force him to eat the smallest amount of food. He loses a ton of weight and really doesn't look healthy.

The other day I found out that he weighs himself every single day when he's at his house and if he goes even a tiny bit over his set weight he "compensates" for it by not eating until he's back to where he wants to be. When he stays over mine he doesn't weigh which causes him to gain more weight and so he'll go longer periods of time without eating to get back where he wants to be.

I'm seriously concerned that he has some type of bulimia. I'm worried it's going to get worse or that he's going to make himself faint by going so long without food. I've tried talking to him about it but he gets very defensive and starts calling himself fat. I don't know how to get through to him and just get him to start eating healthy to maintain a healthy weight rather than binging and then fasting.