Yes, Bellatrix was Voldemort's most loyal follower and one of his strongest. Of course he would be upset over losing her. She was a valuable asset.

Voldemort is incapable of love (implied because he was conceived while his father was under the influence of a love potion). He and Bellatrix had Delphi because having a biological heir would be beneficial to him, and because of his obsession of being immortal, he possibly saw having his bloodline continue as a form of pseudo-immortality (many people actually see things this way). It's also possible that it was a reward of sorts for Bellatrix's loyalty.

Voldemort couldn't love due to his upbringing, not because of the love potion. It's a common misconceptio.n

No, I believe that Rowling said that his father being under a love potion contributed to it. It was originally just a fan-theory, but Rowing confirmed it. Voldemort is a sociopath because of his upbringing, but his inability to love or even understand love is a result of his conception while under a love potion.

Its bc of both things to me *shruggie*

Just disregard the cursed child and rest easy.