Anger = Healing?

[Livin4ME]

ok guys, I'm having issues with S3. Hoping ya'll can give me some insight on how to handle it.
When he comes back from spending time with stbx, he wets the bed at night and will have random accidents during the day. He's been potty trained for a while now and sometimes he would have accidents, but they've become more frequent in the last couple months. And I've noticed that it's usually the 2nd, 3rd, and 4th night after being with stbx. After that, he'll be fine until the next visit. During the day when he has an accident, he'll just stand up from whatever he's doing, and won't even attempt to run to the bathroom, he'll just go.
Also, his tantrums and meltdowns have become more frequent. I know that it's somewhat normal for his age, but at what point does it become 'not normal'!? He's been trying to get me and stbx to hug and kiss, refusing to talk to stbx on the phone when he calls, and has not wanted to go with him when he picks him up. And the smallest thing will set him off in a complete meltdown where he screams and cries for his dad and I can't get him to calm down! Again, I know some of it is 'normal' for the age, but how much of it!? And how to I handle it? I can't keep calling stbx everytime he has a meltdown. Is there something I can do? I try calming him down and I'm calm myself when he does this stuff. Sometimes I do get upset, but more times than not, I'm calm. When he has an accident, I don't get onto him or yell. I tell him it's ok and he tell him next time, he needs to hurry to the bathroom.
I'm just at my wits end with it, ya know. Any advice or suggestions?!