If your faith was lack lustre, surely the Hindu wedding should have been so upsetting to be falling out over all these later.
i am surprised your friends didn’t mention the necklace. Or that the person conducting the ceremony didn’t mention or ask about raising children before.
I don’t think the issue is that you have different religions, per se. Marriages often struggle when one person becomes more religious, if it’s not something the other is involved in.
But I think your problem, is a communication one and a failure to embrace each other’s cultures and religions and compromise. It’s about your points of views.
My mum was a strict Irish Catholic. We still did Yule for example. She came to events. Her thoughts were that God (as in her version of god) had brought my dad too her and blessed her with kids, he wouldn’t be mad for sharing the culture. For being joyous and happy with the family he gave her.
If you think participating at all, on any of his families celebrations and special occasions, is turning your back on God, then surely your marriage is turning your back on God too. I don’t believe any of it is turning your back on him but how can participating in his life be turning your back, but marrying him not be Or do you believe your God is wanting you to convert him? You married to create a family, an extension of your own families, who are different and believe different things.
I think you might need to decide if compromise on this is something you want to do. If it is, counselling may help. Not counselling set up by a religious organisation, probably.
If you can’t, I think you may need to end this marriage and peruse a marriage within your own religion.
But you need this sorting before you have kids.