I've read numerous posts in regards to everyone cursing Shiv, and Ipshita and their respective moms. I'm not saying that what they did was right, or favouring their behaviour towards Gauri.
This is just my take, and my understanding of Shiv, and his "love".
As Shiv explained to Gauri on the night that they were kidnapped that when he fell in love he was young, and that perhaps he never understood what love was or is.
Shiv grew up with Ipshita, her being there with him every step of the way, pulling him out of trouble and covering for him. He feels that this is the girl he loves, and wants to marry, but can not because of his Kundali's dosh. He doesn't believe in it but Sugna (for someone who doesn't believe in fate and tries to make her own karam) doesn't want to live with the possibility of harming a child hatches a plan with Nikhila, for their own children's happiness to get Shiv married to someone else.
Shiv from initial disagrees to this, and wants no part in this plan (him refusing because he hates Gauri.) Shiv goes into marriage hating Gauri, he doesn't want to marry her, and gives her plenty of chances to leave (As Karam would have it Gauri can't because she has always been obliged to her father). Shiv's anger on Gauri is example of his frustration. He tells Gauri when he starts liking her, that he doesn't know why he removes his anger on her or has never been nice to her, it is because he is frustrated that fate is not allowing him to be with someone he loves, which is Ipshita.
As Shiv sees Gauri's sacrifice for him and her family, he begins to question his own love to Ipshita. He thinks that he has grown up loving the portrait, Ipshita, and thought that marriage should only be based on true love and nothing else, but Gauri putting up with Shiv, has made Shiv realize that what he did was wrong. Seeing her love for him, that she is also able to die for him, has Shiv torn. He wanted Gauri to leave his life, also have a chance in love (hence him bringing back Shashank) but Gauri fell in love with him, throwing him in a predicament. He tells Gauri that even though she loves him, he can't love her back, he loves someone else. He can't reveal who it is because he doesn't want Gauri to be hurt by the truth. He tries to be nice to her and tells her to go away for him, but it is Gauri who keeps on coming back to him.
Shiv believes he loves Ipshita, because that is the only love he has known, they having grown together. Ipshita loves Shiv too, but she also realizes that Gauri has become a part of Shiv. (When she questions Anupam about love, it is because even she questions her actions and her love for Shiv. She asks shiv if he misses Gauri). Gauri in her unconditional love for Shiv, wanting to be with him despite her imminent death, has actually shown Shiv what love is.
He believes he loves Ipshita, but I think the way he said it betrays his true emotions. For Ipshita what he feels is passion and he told her that he worships Ipshita...but when he is with Gauri, he feels comfort and feel like giving comfort to Gauri, and protecting her. He can't hurt Gauri, and can't bear her tears. He feels Gauri's pain but never claims to understand or feeling what Ipshita feels when seeing him with Gauri.
I think that Shiv has placed Ipshita from childhood on a pedestal which he believes is love, but will soon realize that worshipping Ipshita, the way he said it isn't love for Ipshita. In fact I think the way that Shiv compared Ipshita to Gauri makes it more obvious that Shiv unknowningly feels more for Gauri than Ipshita. (He can't see her pain, or can't see hatred in her eyes for him.)
As for Ipshita, I think if she truly loved Shiv, she should have married him despite his Kundali or what her mother felt. She shouldn't have let Gauri suffer, and in that I think that she is the most selfish of all of them. Shiv, could care less about his Kundali, and I do not hate him for loving Ipshita, but while Shiv is not completely faultless, he has become trapped between his mom's emotional blackmailin, his love for Ipshita, and Gauri's love for him, and actually I feel completely bad that he is in a bad place altogether.
I do think that Shiv though should let Gauri know he loves Ipshita, and do believe that he shouldn't have kissed Ipshita (he is married), or broken her fast, but I don't think that Shiv is completely evil and selfish.
I know I said a lot, please don't attack me, it is just how I feel, and I think that Shiv will realize that what he feels for Gauri is more than what he feels for Ipshita.
"Where love reigns even the impossible can be attained, and love goes against all odds."
Shiv was meant to be with Gauri, even gods can go against that match.