Your marriage doesn't have to be a boring, passionless existence. You can have the excitement of romance and intimacy that you lost at the beginning. Here is how to start.
1. You have to choose to make it happen. I was in a human relations course and the instructor said, "I can't embarrass you. You choose to be embarrassed." As ridiculous as that sounded to me at the moment, the more I thought about it, the more I realized he was right. If someone attempts to humiliate me or anger me or draw out any emotional response from me, I have to choose to make that emotional response. The entertainment industry constantly attempts to elicit an emotional response from its audience, but if you're not in the mood to be glad when they want you to be glad, laugh when they are funny, cry when they are being sad, then you are choosing not to be that way. The opposite can be true. You can be watching a movie and at some gut-wrenching, emotional climax, someone near you can choose to be funny and crack a joke.
2. Love is a choice. You have to decide you're going to love your spouse regardless of whether or not any affection is returned. You have to be prepared to have your initiatives intentionally or unintentionally ignored or misinterpreted. You have to choose not to be hurt or sulk. You have to choose to try again.
3. You have to choose to take the initiative. If your marriage is stale because your spouse never takes the initiative any more, it's going to stay that way. It is very doubtful that your spouse will suddenly wake up one day and think, "I want to be romantic today and be passionate about the person I married." No. If something is going to change, it's going to have to start with you.
4. Emotions follow actions. You may feel like you can't be passionate anymore. The old feelings are long gone. There really aren't any embers there to rekindle. Make the advances. Plan something romantic and then do it. Try something you used to do when you first dated that was fun. If the plan fails, try again or try something different. If it succeeds, do more. Eventually, those old feelings will return.
5. I'm not here to recommend specific romantic things to try like a walk on the beach, candlelight dinner, romantic music, etc. Rekindling your marriage is about the way you think about yourself, your spouse, your relationship, and marriage itself. It's about understanding why you fell bored, hurt, depressed, isolated, and alone. I recommend a couple of really good books to help you work through your thought processes and thus better equip you to understand yourself so that you are better capable of reigniting the cold embers of marital love. One is Rekindled by Pat and Jill Williams. The other is Love Life for Every Married Couple by Dr. Ed Wheat.
Have the courage to go for it. It will be worth the effort. After all, you have to choose. Do you want your marriage to continue the way it is now or do you want it to improve? Only you can make that first step happen.