1. How can I get him to be interested in me again?
While it might seem contrary to common sense, getting your husband to be interested in you again after he's having an affair with another woman is actually dependent on your actions, not his.
You have to change your own actions, and take charge of your own life. Look at it this way: your husband has decided to turn his attention to another woman, so you no longer owe him anything. You can do what you want now.
When you take this attitude, you will become more authoritative and attractive. People are drawn to those who are free-spirited, or who do what they want. If you start doing the things you want with no regard to what your husband thinks anymore, you will automatically gain his interest.
2. How can I deal with the pain?
It is painful to know your husband's fallen for someone else, but know this: often we think we're in love with someone, when in reality, this feeling results from an unmet need within ourselves.
Your husband is probably infatuated with this other woman because she's new and exciting and gives him feelings of passion. But you can respark that passion within your own marriage once you start to live your own free life, doing the things you want.
This doesn't mean neglecting family or the kids or anything; it just means taking charge of your destiny. You don't have to think of yourself as sacrificing everything for what other people want of you.
Make a list of your hobbies and passions. Take steps to get involved in them - even if it's as simple as painting, crafting, knitting, whatever you might be interested in. But don't do anything just because you think it's expected of you. Do what you really want to.
This will have the side benefit of distracting you from your husband's affair.
3. Will we ever reconnect and have that spark again?
Yes, you can have the spark of passion back with your husband, but it's dependent on you. He has lost interest, so you must be the instigator.
Start by pursuing your own interests and passions. As time progresses, he will gradually lose interest in this other woman, especially if he sees you doing what you want to do. (While this may not always be the case depending on the marriage, it's often true that couples just lose the spark because one of them isn't happy.)
When your husband's interest in you starts to return, it's very important that you continue to live the life you want, doing the things you want, so that he'll see you as the object of his desire.