If his mother regretted giving birth to him because he left her religion, she's not a mother at all. Love is unconditional, and we don't stop loving someone just because they disagree with us. If his mother did that, good riddance to her. That's the outlook of someone who is worthless.
Again, this is YOUR belief. He doesn't believe in hell, nor do millions and millions of other people. Don't try those scare tactics, they aren't compatible with morality.
Haven't you figured it out? He said he left Islam. He's not your brother. And don't say "forgive me," and then try to scare him. That's not asking for forgiveness, that's being an ass.
This isn't about your faith and stop trying to convert him. STOP. It's common decency. You don't see anyone else going around SHOVING their beliefs down your throat, so kindly don't do it to anyone else.
In other words, grow up and leave him alone.
I think your post just shows your mentality.. all he tried to do was give him reasons from his own understanding of what could happen. Yes a mothers love is unconditional but that mother also loves the fact that her son is muslim (your mother might not care but most mothers do) so for the sake of her happiness he can avoid telling her that.