How Can I Show Him I Love After 35 Years of Marriage?
Just come up with a way to make him smile every day. Thank him when he is great with you. Be great with him. Get curious about him. Come from the notion that you don't really know this person, and it's your mission to find out. Ask him to share with you the stuff he never did, or that he thought might be too stupid. Ask him if there is anything he wants to get off his chest, and what you can do to make his life better.
In other words, just communicate. He's your husband. Take your partnership to the next level.
And it could be you make him a birthday party, or a party for no reason. Invite every one you know who knows him to share something and make him a little book. I did this for my wife. The online version is here, Sharleen's Special Page. The paper version is ten times better.
How do I Know He Still Loves Me After 35 Years?
How do you know he ever loved you? What does it matter anyway?
A better question might be “Are you willing to take responsibility for making life together with him great?”
If so, you can restart the romance, plan a little getaway, buy a little gift, engage in a hundred small acts of kindness, not get upset. He might just get that that is a great way to be and start to surprise you back.
Maybe try waking up every morning, and saying to yourself “there's something new to discover about this man,” and “there's a way I can make him smile that he's never smiled before.” If you start looking for those things, you might find you still have a lifetime of adventures to pursue with this person.